Improve various things in the checksum code

- Size flist checksum data to hold the active size, not the max. - Add a negotiated hash method to the daemon auth code. - Use EVP for all openssl digests. This makes it easy to add more openssl digest methods and avoids deprecation warnings. - Support a way to re-enable deprecated digests via openssl conf file and allow a default file to be configured. - Supply a simple openssl-rsync.cnf file to enable legacy digests.
2025-12-23 23:28:17 -05:00 · 2022-09-10 09:43:47 -07:00
parent b8c2fde3a5
commit 7e2711bb2b
18 changed files with 520 additions and 273 deletions
--- a/NEWS.md
+++ b/NEWS.md
@@ -6,6 +6,28 @@

 - ...

+### ENHANCEMENTS:
+
+- Added negotiated daemon-auth support that allows a stronger checksum digest
+  to be used.
+
+### PACKAGING RELATED:
+
+- The checksum code now uses openssl's EVP methods, which gets rid of various
+  deprecation warnings and makes it easy to support more digest methods.  On
+  newer systems, the MD4 digest is marked as legacy in the openssl code, which
+  makes openssl refuse to support it via EVP.  You can just ignore this and
+  allow the included MD4 code to be used for older rsync connections (when
+  talking to an rsync prior to 3.0.0) or you can configure rsync to tell
+  openssl to enable legacy algorithms (see below).
+
+- A simple openssl config file is supplied that can be optionally installed for
+  rsync to use.  If you install packaging/openssl-rsync.cnf to a public spot
+  (such as ` /etc/ssl/openssl-rsync.cnf` or similar) and then configure rsync
+  using `--with-openssl-conf=/path/name.cnf`, this will cause rsync to export
+  the configured path in the OPENSSL_CONF environment variable (when it is not
+  already set).  This will enable openssl's MD4 code for rsync to use.
+
 ------------------------------------------------------------------------------

 # NEWS for rsync 3.2.6 (9 Sep 2022)
--- a/authenticate.c
+++ b/authenticate.c
@@ -24,6 +24,7 @@

 extern int read_only;
 extern char *password_file;
+extern struct name_num_obj valid_auth_checksums;

 /***************************************************************************
 encode a buffer using base64 - simple and slow algorithm. null terminates
@@ -72,9 +73,9 @@ static void gen_challenge(const char *addr, char *challenge)
 	SIVAL(input, 20, tv.tv_usec);
 	SIVAL(input, 24, getpid());

-	sum_init(-1, 0);
+	len = sum_init(valid_auth_checksums.negotiated_nni, 0);
 	sum_update(input, sizeof input);
-	len = sum_end(digest);
+	sum_end(digest);

 	base64_encode(digest, len, challenge, 0);
 }
@@ -86,10 +87,10 @@ static void generate_hash(const char *in, const char *challenge, char *out)
 	char buf[MAX_DIGEST_LEN];
 	int len;

-	sum_init(-1, 0);
+	len = sum_init(valid_auth_checksums.negotiated_nni, 0);
 	sum_update(in, strlen(in));
 	sum_update(challenge, strlen(challenge));
-	len = sum_end(buf);
+	sum_end(buf);

 	base64_encode(buf, len, out, 0);
 }
@@ -238,6 +239,7 @@ char *auth_server(int f_in, int f_out, int module, const char *host,
 	if (!users || !*users)
 		return "";

+	negotiate_daemon_auth(f_out, 0);
 	gen_challenge(addr, challenge);

 	io_printf(f_out, "%s%s\n", leader, challenge);
@@ -350,6 +352,7 @@ void auth_client(int fd, const char *user, const char *challenge)

 	if (!user || !*user)
 		user = "nobody";
+	negotiate_daemon_auth(-1, 1);

 	if (!(pass = getpassf(password_file))
 	 && !(pass = getenv("RSYNC_PASSWORD"))) {
--- a/checksum.c
+++ b/checksum.c
@@ -42,49 +42,82 @@ extern int protocol_version;
 extern int proper_seed_order;
 extern const char *checksum_choice;

+#define NNI_BUILTIN (1<<0)
+#define NNI_EVP (1<<1)
+#define NNI_EVP_OK (1<<2)
+
 struct name_num_item valid_checksums_items[] = {
 #ifdef SUPPORT_XXH3
-	{ CSUM_XXH3_128, "xxh128", NULL },
-	{ CSUM_XXH3_64, "xxh3", NULL },
+	{ CSUM_XXH3_128, 0, "xxh128", NULL },
+	{ CSUM_XXH3_64, 0, "xxh3", NULL },
 #endif
 #ifdef SUPPORT_XXHASH
-	{ CSUM_XXH64, "xxh64", NULL },
-	{ CSUM_XXH64, "xxhash", NULL },
+	{ CSUM_XXH64, 0, "xxh64", NULL },
+	{ CSUM_XXH64, 0, "xxhash", NULL },
 #endif
-	{ CSUM_MD5, "md5", NULL },
-	{ CSUM_MD4, "md4", NULL },
-	{ CSUM_NONE, "none", NULL },
-	{ 0, NULL, NULL }
+	{ CSUM_MD5, NNI_BUILTIN|NNI_EVP, "md5", NULL },
+	{ CSUM_MD4, NNI_BUILTIN|NNI_EVP, "md4", NULL },
+	{ CSUM_NONE, 0, "none", NULL },
+	{ 0, 0, NULL, NULL }
 };

 struct name_num_obj valid_checksums = {
-	"checksum", NULL, NULL, 0, 0, valid_checksums_items
+	"checksum", NULL, 0, 0, valid_checksums_items
 };

-int xfersum_type = 0; /* used for the file transfer checksums */
-int checksum_type = 0; /* used for the pre-transfer (--checksum) checksums */
+struct name_num_item valid_auth_checksums_items[] = {
+	{ CSUM_MD5, NNI_BUILTIN|NNI_EVP, "md5", NULL },
+	{ CSUM_MD4, NNI_BUILTIN|NNI_EVP, "md4", NULL },
+	{ 0, 0, NULL, NULL }
+};

+struct name_num_obj valid_auth_checksums = {
+	"daemon auth checksum", NULL, 0, 0, valid_auth_checksums_items
+};
+
+/* These cannot make use of openssl, so they're marked just as built-in */
+struct name_num_item implied_checksum_md4 =
+    { CSUM_MD4, NNI_BUILTIN, "md4", NULL };
+struct name_num_item implied_checksum_md5 =
+    { CSUM_MD5, NNI_BUILTIN, "md5", NULL };
+
+struct name_num_item *xfer_sum_nni; /* used for the transfer checksum2 computations */
+const EVP_MD *xfer_sum_evp_md;
+int xfer_sum_len;
+struct name_num_item *file_sum_nni; /* used for the pre-transfer --checksum computations */
+const EVP_MD *file_sum_evp_md;
+int file_sum_len;
+
+#ifdef USE_OPENSSL
+EVP_MD_CTX *ctx_evp = NULL;
+#endif
 static int initialized_choices = 0;

-int parse_csum_name(const char *name, int len)
+struct name_num_item *parse_csum_name(const char *name, int len)
 {
 	struct name_num_item *nni;

 	if (len < 0 && name)
 		len = strlen(name);

-	if (!name || (len == 4 && strncasecmp(name, "auto", 4) == 0)) {
-		if (protocol_version >= 30)
-			return CSUM_MD5;
-		if (protocol_version >= 27)
-			return CSUM_MD4_OLD;
-		if (protocol_version >= 21)
-			return CSUM_MD4_BUSTED;
-		return CSUM_MD4_ARCHAIC;
-	}
+	init_checksum_choices();

-	if (!initialized_choices)
-		init_checksum_choices();
+	if (!name || (len == 4 && strncasecmp(name, "auto", 4) == 0)) {
+		if (protocol_version >= 30) {
+			if (!proper_seed_order)
+				return &implied_checksum_md5;
+			name = "md5";
+			len = 3;
+		} else {
+			if (protocol_version >= 27)
+				implied_checksum_md4.num = CSUM_MD4_OLD;
+			else if (protocol_version >= 21)
+				implied_checksum_md4.num = CSUM_MD4_BUSTED;
+			else
+				implied_checksum_md4.num = CSUM_MD4_ARCHAIC;
+			return &implied_checksum_md4;
+		}
+	}

 	nni = get_nni_by_name(&valid_checksums, name, len);

@@ -93,44 +126,72 @@ int parse_csum_name(const char *name, int len)
 		exit_cleanup(RERR_UNSUPPORTED);
 	}

-	return nni->num;
+	return nni;
 }

-static const char *checksum_name(int num)
+static const EVP_MD *csum_evp_md(struct name_num_item *nni)
 {
-	struct name_num_item *nni = get_nni_by_num(&valid_checksums, num);
+#ifdef USE_OPENSSL
+	const EVP_MD *emd;
+	if (!(nni->flags & NNI_EVP))
+		return NULL;

-	return nni ? nni->name : num < CSUM_MD4 ? "md4" : "UNKNOWN";
+#ifdef USE_MD5_ASM
+	if (nni->num == CSUM_MD5)
+		emd = NULL;
+	else
+#endif
+		emd = EVP_get_digestbyname(nni->name);                                               
+	if (emd && !(nni->flags & NNI_EVP_OK)) { /* Make sure it works before we advertise it */
+		if (!ctx_evp && !(ctx_evp = EVP_MD_CTX_create()))
+			out_of_memory("csum_evp_md");
+		/* Some routines are marked as legacy and are not enabled in the openssl.cnf file.
+		 * If we can't init the emd, we'll fall back to our built-in code. */
+		if (EVP_DigestInit_ex(ctx_evp, emd, NULL) == 0)
+			emd = NULL;
+		else
+			nni->flags = (nni->flags & ~NNI_BUILTIN) | NNI_EVP_OK;
+	}
+	if (!emd)
+		nni->flags &= ~NNI_EVP;
+	return emd;
+#else
+	return NULL;
+#endif
 }

 void parse_checksum_choice(int final_call)
 {
-	if (valid_checksums.negotiated_name)
-		xfersum_type = checksum_type = valid_checksums.negotiated_num;
+	if (valid_checksums.negotiated_nni)
+		xfer_sum_nni = file_sum_nni = valid_checksums.negotiated_nni;
 	else {
 		char *cp = checksum_choice ? strchr(checksum_choice, ',') : NULL;
 		if (cp) {
-			xfersum_type = parse_csum_name(checksum_choice, cp - checksum_choice);
-			checksum_type = parse_csum_name(cp+1, -1);
+			xfer_sum_nni = parse_csum_name(checksum_choice, cp - checksum_choice);
+			file_sum_nni = parse_csum_name(cp+1, -1);
 		} else
-			xfersum_type = checksum_type = parse_csum_name(checksum_choice, -1);
+			xfer_sum_nni = file_sum_nni = parse_csum_name(checksum_choice, -1);
 		if (am_server && checksum_choice)
-			validate_choice_vs_env(NSTR_CHECKSUM, xfersum_type, checksum_type);
+			validate_choice_vs_env(NSTR_CHECKSUM, xfer_sum_nni->num, file_sum_nni->num);
 	}
+	xfer_sum_len = csum_len_for_type(xfer_sum_nni->num, 0);
+	file_sum_len = csum_len_for_type(file_sum_nni->num, 0);
+	xfer_sum_evp_md = csum_evp_md(xfer_sum_nni);
+	file_sum_evp_md = csum_evp_md(file_sum_nni);

-	if (xfersum_type == CSUM_NONE)
+	if (xfer_sum_nni->num == CSUM_NONE)
 		whole_file = 1;

 	/* Snag the checksum name for both write_batch's option output & the following debug output. */
-	if (valid_checksums.negotiated_name)
-		checksum_choice = valid_checksums.negotiated_name;
+	if (valid_checksums.negotiated_nni)
+		checksum_choice = valid_checksums.negotiated_nni->name;
 	else if (checksum_choice == NULL)
-		checksum_choice = checksum_name(xfersum_type);
+		checksum_choice = xfer_sum_nni->name;

 	if (final_call && DEBUG_GTE(NSTR, am_server ? 3 : 1)) {
 		rprintf(FINFO, "%s%s checksum: %s\n",
 			am_server ? "Server" : "Client",
-			valid_checksums.negotiated_name ? " negotiated" : "",
+			valid_checksums.negotiated_nni ? " negotiated" : "",
 			checksum_choice);
 	}
 }
@@ -211,7 +272,22 @@ uint32 get_checksum1(char *buf1, int32 len)

 void get_checksum2(char *buf, int32 len, char *sum)
 {
-	switch (xfersum_type) {
+#ifdef USE_OPENSSL
+	if (xfer_sum_evp_md) {
+		static EVP_MD_CTX *evp = NULL;
+		uchar seedbuf[4];
+		if (!evp && !(evp = EVP_MD_CTX_create()))
+			out_of_memory("get_checksum2");
+		EVP_DigestInit_ex(evp, xfer_sum_evp_md, NULL);
+		if (checksum_seed) {
+			SIVALu(seedbuf, 0, checksum_seed);
+			EVP_DigestUpdate(evp, seedbuf, 4);
+		}
+		EVP_DigestUpdate(evp, (uchar *)buf, len);
+		EVP_DigestFinal_ex(evp, (uchar *)sum, NULL);
+	} else
+#endif
+	switch (xfer_sum_nni->num) {
 #ifdef SUPPORT_XXHASH
 	  case CSUM_XXH64:
 		SIVAL64(sum, 0, XXH64(buf, len, checksum_seed));
@@ -229,7 +305,7 @@ void get_checksum2(char *buf, int32 len, char *sum)
 	  }
 #endif
 	  case CSUM_MD5: {
-		md5_context m5;
+		md_context m5;
 		uchar seedbuf[4];
 		md5_begin(&m5);
 		if (proper_seed_order) {
@@ -249,20 +325,6 @@ void get_checksum2(char *buf, int32 len, char *sum)
 		break;
 	  }
 	  case CSUM_MD4:
-#ifdef USE_OPENSSL
-	  {
-		MD4_CTX m4;
-		MD4_Init(&m4);
-		MD4_Update(&m4, (uchar *)buf, len);
-		if (checksum_seed) {
-			uchar seedbuf[4];
-			SIVALu(seedbuf, 0, checksum_seed);
-			MD4_Update(&m4, seedbuf, 4);
-		}
-		MD4_Final((uchar *)sum, &m4);
-		break;
-	  }
-#endif
 	  case CSUM_MD4_OLD:
 	  case CSUM_MD4_BUSTED:
 	  case CSUM_MD4_ARCHAIC: {
@@ -295,7 +357,7 @@ void get_checksum2(char *buf, int32 len, char *sum)
 		 * are multiples of 64.  This is fixed by calling mdfour_update()
 		 * even when there are no more bytes.
 		 */
-		if (len - i > 0 || xfersum_type > CSUM_MD4_BUSTED)
+		if (len - i > 0 || xfer_sum_nni->num > CSUM_MD4_BUSTED)
 			mdfour_update(&m, (uchar *)(buf1+i), len-i);

 		mdfour_result(&m, (uchar *)sum);
@@ -313,15 +375,33 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 	int32 remainder;
 	int fd;

-	memset(sum, 0, MAX_DIGEST_LEN);
-
 	fd = do_open(fname, O_RDONLY, 0);
-	if (fd == -1)
+	if (fd == -1) {
+		memset(sum, 0, file_sum_len);
 		return;
+	}

 	buf = map_file(fd, len, MAX_MAP_SIZE, CHUNK_SIZE);

-	switch (checksum_type) {
+#ifdef USE_OPENSSL
+	if (file_sum_evp_md) {
+		static EVP_MD_CTX *evp = NULL;
+		if (!evp && !(evp = EVP_MD_CTX_create()))
+			out_of_memory("file_checksum");
+
+		EVP_DigestInit_ex(evp, file_sum_evp_md, NULL);
+
+		for (i = 0; i + CHUNK_SIZE <= len; i += CHUNK_SIZE)
+			EVP_DigestUpdate(evp, (uchar *)map_ptr(buf, i, CHUNK_SIZE), CHUNK_SIZE);
+
+		remainder = (int32)(len - i);
+		if (remainder > 0)
+			EVP_DigestUpdate(evp, (uchar *)map_ptr(buf, i, remainder), remainder);
+
+		EVP_DigestFinal_ex(evp, (uchar *)sum, NULL);
+	} else
+#endif
+	switch (file_sum_nni->num) {
 #ifdef SUPPORT_XXHASH
 	  case CSUM_XXH64: {
 		static XXH64_state_t* state = NULL;
@@ -381,7 +461,7 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 	  }
 #endif
 	  case CSUM_MD5: {
-		md5_context m5;
+		md_context m5;

 		md5_begin(&m5);

@@ -396,23 +476,6 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 		break;
 	  }
 	  case CSUM_MD4:
-#ifdef USE_OPENSSL
-	  {
-		MD4_CTX m4;
-
-		MD4_Init(&m4);
-
-		for (i = 0; i + CHUNK_SIZE <= len; i += CHUNK_SIZE)
-			MD4_Update(&m4, (uchar *)map_ptr(buf, i, CHUNK_SIZE), CHUNK_SIZE);
-
-		remainder = (int32)(len - i);
-		if (remainder > 0)
-			MD4_Update(&m4, (uchar *)map_ptr(buf, i, remainder), remainder);
-
-		MD4_Final((uchar *)sum, &m4);
-		break;
-	  }
-#endif
 	  case CSUM_MD4_OLD:
 	  case CSUM_MD4_BUSTED:
 	  case CSUM_MD4_ARCHAIC: {
@@ -428,7 +491,7 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 		 * are multiples of 64.  This is fixed by calling mdfour_update()
 		 * even when there are no more bytes. */
 		remainder = (int32)(len - i);
-		if (remainder > 0 || checksum_type > CSUM_MD4_BUSTED)
+		if (remainder > 0 || file_sum_nni->num > CSUM_MD4_BUSTED)
 			mdfour_update(&m, (uchar *)map_ptr(buf, i, remainder), remainder);

 		mdfour_result(&m, (uchar *)sum);
@@ -436,7 +499,7 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 	  }
 	  default:
 		rprintf(FERROR, "Invalid checksum-choice for --checksum: %s (%d)\n",
-			checksum_name(checksum_type), checksum_type);
+			file_sum_nni->name, file_sum_nni->num);
 		exit_cleanup(RERR_UNSUPPORTED);
 	}

@@ -445,30 +508,35 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 }

 static int32 sumresidue;
-static union {
-	md_context md;
-#ifdef USE_OPENSSL
-	MD4_CTX m4;
-#endif
-	md5_context m5;
-} ctx;
+static md_context ctx_md;
 #ifdef SUPPORT_XXHASH
 static XXH64_state_t* xxh64_state;
 #endif
 #ifdef SUPPORT_XXH3
 static XXH3_state_t* xxh3_state;
 #endif
-static int cursum_type;
+static struct name_num_item *cur_sum_nni;
+static const EVP_MD *cur_sum_evp_md;
+int cur_sum_len;

-void sum_init(int csum_type, int seed)
+int sum_init(struct name_num_item *nni, int seed)
 {
 	char s[4];

-	if (csum_type < 0)
-		csum_type = parse_csum_name(NULL, 0);
-	cursum_type = csum_type;
+	if (!nni)
+		nni = parse_csum_name(NULL, 0);
+	cur_sum_nni = nni;
+	cur_sum_len = csum_len_for_type(nni->num, 0);
+	cur_sum_evp_md = csum_evp_md(nni);

-	switch (csum_type) {
+#ifdef USE_OPENSSL
+	if (cur_sum_evp_md) {
+		if (!ctx_evp && !(ctx_evp = EVP_MD_CTX_create()))
+			out_of_memory("file_checksum");
+		EVP_DigestInit_ex(ctx_evp, cur_sum_evp_md, NULL);
+	} else
+#endif
+	switch (cur_sum_nni->num) {
 #ifdef SUPPORT_XXHASH
 	  case CSUM_XXH64:
 		if (!xxh64_state && !(xxh64_state = XXH64_createState()))
@@ -489,20 +557,16 @@ void sum_init(int csum_type, int seed)
 		break;
 #endif
 	  case CSUM_MD5:
-		md5_begin(&ctx.m5);
+		md5_begin(&ctx_md);
 		break;
 	  case CSUM_MD4:
-#ifdef USE_OPENSSL
-		MD4_Init(&ctx.m4);
-#else
-		mdfour_begin(&ctx.md);
+		mdfour_begin(&ctx_md);
 		sumresidue = 0;
-#endif
 		break;
 	  case CSUM_MD4_OLD:
 	  case CSUM_MD4_BUSTED:
 	  case CSUM_MD4_ARCHAIC:
-		mdfour_begin(&ctx.md);
+		mdfour_begin(&ctx_md);
 		sumresidue = 0;
 		SIVAL(s, 0, seed);
 		sum_update(s, 4);
@@ -512,6 +576,8 @@ void sum_init(int csum_type, int seed)
 	  default: /* paranoia to prevent missing case values */
 		exit_cleanup(RERR_UNSUPPORTED);
 	}
+
+	return cur_sum_len;
 }

 /**
@@ -524,7 +590,12 @@ void sum_init(int csum_type, int seed)
 **/
 void sum_update(const char *p, int32 len)
 {
-	switch (cursum_type) {
+#ifdef USE_OPENSSL
+	if (cur_sum_evp_md) {
+		EVP_DigestUpdate(ctx_evp, (uchar *)p, len);
+	} else
+#endif
+	switch (cur_sum_nni->num) {
 #ifdef SUPPORT_XXHASH
 	  case CSUM_XXH64:
 		XXH64_update(xxh64_state, p, len);
@@ -539,39 +610,35 @@ void sum_update(const char *p, int32 len)
 		break;
 #endif
 	  case CSUM_MD5:
-		md5_update(&ctx.m5, (uchar *)p, len);
+		md5_update(&ctx_md, (uchar *)p, len);
 		break;
 	  case CSUM_MD4:
-#ifdef USE_OPENSSL
-		MD4_Update(&ctx.m4, (uchar *)p, len);
-		break;
-#endif
 	  case CSUM_MD4_OLD:
 	  case CSUM_MD4_BUSTED:
 	  case CSUM_MD4_ARCHAIC:
 		if (len + sumresidue < CSUM_CHUNK) {
-			memcpy(ctx.md.buffer + sumresidue, p, len);
+			memcpy(ctx_md.buffer + sumresidue, p, len);
 			sumresidue += len;
 			break;
 		}

 		if (sumresidue) {
 			int32 i = CSUM_CHUNK - sumresidue;
-			memcpy(ctx.md.buffer + sumresidue, p, i);
-			mdfour_update(&ctx.md, (uchar *)ctx.md.buffer, CSUM_CHUNK);
+			memcpy(ctx_md.buffer + sumresidue, p, i);
+			mdfour_update(&ctx_md, (uchar *)ctx_md.buffer, CSUM_CHUNK);
 			len -= i;
 			p += i;
 		}

 		while (len >= CSUM_CHUNK) {
-			mdfour_update(&ctx.md, (uchar *)p, CSUM_CHUNK);
+			mdfour_update(&ctx_md, (uchar *)p, CSUM_CHUNK);
 			len -= CSUM_CHUNK;
 			p += CSUM_CHUNK;
 		}

 		sumresidue = len;
 		if (sumresidue)
-			memcpy(ctx.md.buffer, p, sumresidue);
+			memcpy(ctx_md.buffer, p, sumresidue);
 		break;
 	  case CSUM_NONE:
 		break;
@@ -580,13 +647,18 @@ void sum_update(const char *p, int32 len)
 	}
 }

-/* NOTE: all the callers of sum_end() pass in a pointer to a buffer that is
- * MAX_DIGEST_LEN in size, so even if the csum-len is shorter than that (i.e.
- * CSUM_MD4_ARCHAIC), we don't have to worry about limiting the data we write
- * into the "sum" buffer. */
-int sum_end(char *sum)
+/* The sum buffer only needs to be as long as the current checksum's digest
+ * len, not MAX_DIGEST_LEN. Note that for CSUM_MD4_ARCHAIC that is the full
+ * MD4_DIGEST_LEN even if the file-list code is going to ignore all but the
+ * first 2 bytes of it. */
+void sum_end(char *sum)
 {
-	switch (cursum_type) {
+#ifdef USE_OPENSSL
+	if (cur_sum_evp_md) {
+		EVP_DigestFinal_ex(ctx_evp, (uchar *)sum, NULL);
+	} else
+#endif
+	switch (cur_sum_nni->num) {
 #ifdef SUPPORT_XXHASH
 	  case CSUM_XXH64:
 		SIVAL64(sum, 0, XXH64_digest(xxh64_state));
@@ -604,22 +676,18 @@ int sum_end(char *sum)
 	  }
 #endif
 	  case CSUM_MD5:
-		md5_result(&ctx.m5, (uchar *)sum);
+		md5_result(&ctx_md, (uchar *)sum);
 		break;
 	  case CSUM_MD4:
-#ifdef USE_OPENSSL
-		MD4_Final((uchar *)sum, &ctx.m4);
-		break;
-#endif
 	  case CSUM_MD4_OLD:
-		mdfour_update(&ctx.md, (uchar *)ctx.md.buffer, sumresidue);
-		mdfour_result(&ctx.md, (uchar *)sum);
+		mdfour_update(&ctx_md, (uchar *)ctx_md.buffer, sumresidue);
+		mdfour_result(&ctx_md, (uchar *)sum);
 		break;
 	  case CSUM_MD4_BUSTED:
 	  case CSUM_MD4_ARCHAIC:
 		if (sumresidue)
-			mdfour_update(&ctx.md, (uchar *)ctx.md.buffer, sumresidue);
-		mdfour_result(&ctx.md, (uchar *)sum);
+			mdfour_update(&ctx_md, (uchar *)ctx_md.buffer, sumresidue);
+		mdfour_result(&ctx_md, (uchar *)sum);
 		break;
 	  case CSUM_NONE:
 		*sum = '\0';
@@ -627,34 +695,72 @@ int sum_end(char *sum)
 	  default: /* paranoia to prevent missing case values */
 		exit_cleanup(RERR_UNSUPPORTED);
 	}
-
-	return csum_len_for_type(cursum_type, 0);
 }

+#if defined SUPPORT_XXH3 || defined USE_OPENSSL
+static void verify_digest(struct name_num_item *nni, BOOL check_auth_list)
+{
+#ifdef SUPPORT_XXH3
+	static int xxh3_result = 0;
+#endif
+#ifdef USE_OPENSSL
+	static int prior_num = 0, prior_flags = 0, prior_result = 0;
+#endif
+
+#ifdef SUPPORT_XXH3
+	if (nni->num == CSUM_XXH3_64 || nni->num == CSUM_XXH3_128) {
+		if (!xxh3_result) {
+			char buf[32816];
+			int j;
+			for (j = 0; j < (int)sizeof buf; j++)
+				buf[j] = ' ' + (j % 96);
+			sum_init(nni, 0);
+			sum_update(buf, 32816);
+			sum_update(buf, 31152);
+			sum_update(buf, 32474);
+			sum_update(buf, 9322);
+			xxh3_result = XXH3_64bits_digest(xxh3_state) != 0xadbcf16d4678d1de ? -1 : 1;
+		}
+		if (xxh3_result < 0)
+			nni->num = CSUM_gone;
+		return;
+	}
+#endif
+
+#ifdef USE_OPENSSL
+	if (BITS_SETnUNSET(nni->flags, NNI_EVP, NNI_BUILTIN|NNI_EVP_OK)) {
+		if (nni->num == prior_num && nni->flags == prior_flags) {
+			nni->flags = prior_result;
+			if (!(nni->flags & NNI_EVP))
+				nni->num = CSUM_gone;
+		} else {
+			prior_num = nni->num;
+			prior_flags = nni->flags;
+			if (!csum_evp_md(nni))
+				nni->num = CSUM_gone;
+			prior_result = nni->flags;
+			if (check_auth_list && (nni = get_nni_by_num(&valid_auth_checksums, prior_num)) != NULL)
+				verify_digest(nni, False);
+		}
+	}
+#endif
+}
+#endif
+
 void init_checksum_choices()
 {
-#ifdef SUPPORT_XXH3
-	char buf[32816];
-	int j;
-	for (j = 0; j < (int)sizeof buf; j++) {
-		buf[j] = ' ' + (j % 96);
-	}
-	sum_init(CSUM_XXH3_64, 0);
-	sum_update(buf, 32816);
-	sum_update(buf, 31152);
-	sum_update(buf, 32474);
-	sum_update(buf, 9322);
-	if (XXH3_64bits_digest(xxh3_state) != 0xadbcf16d4678d1de) {
-		int t, f;
-		struct name_num_item *nni = valid_checksums.list;
-		for (t = f = 0; nni[f].name; f++) {
-			if (nni[f].num == CSUM_XXH3_64 || nni[f].num == CSUM_XXH3_128)
-				continue;
-			if (t != f)
-				nni[t++] = nni[f];
-		}
-		nni[t].name = NULL;
-	}
+	struct name_num_item *nni;
+
+	if (initialized_choices)
+		return;
+
+#if defined SUPPORT_XXH3 || defined USE_OPENSSL
+	for (nni = valid_checksums.list; nni->name; nni++)
+		verify_digest(nni, True);
+
+	for (nni = valid_auth_checksums.list; nni->name; nni++)
+		verify_digest(nni, False);
 #endif
+
 	initialized_choices = 1;
 }
--- a/clientserver.c
+++ b/clientserver.c
@@ -67,6 +67,7 @@ extern uid_t our_uid;
 extern gid_t our_gid;

 char *auth_user;
+char *daemon_auth_choices;
 int read_only = 0;
 int module_id = -1;
 int pid_file_fd = -1;
@@ -149,13 +150,9 @@ int start_socket_client(char *host, int remote_argc, char *remote_argv[],
 static int exchange_protocols(int f_in, int f_out, char *buf, size_t bufsiz, int am_client)
 {
 	int remote_sub = -1;
-#if SUBPROTOCOL_VERSION != 0
-	int our_sub = protocol_version < PROTOCOL_VERSION ? 0 : SUBPROTOCOL_VERSION;
-#else
-	int our_sub = 0;
-#endif
+	int our_sub = get_subprotocol_version();

-	io_printf(f_out, "@RSYNCD: %d.%d\n", protocol_version, our_sub);
+	output_daemon_greeting(f_out, am_client);
 	if (!am_client) {
 		char *motd = lp_motd_file();
 		if (motd && *motd) {
@@ -197,6 +194,14 @@ static int exchange_protocols(int f_in, int f_out, char *buf, size_t bufsiz, int
 		remote_sub = 0;
 	}

+	daemon_auth_choices = strchr(buf + 9, ' ');
+	if (daemon_auth_choices) {
+		char *cp;
+		daemon_auth_choices = strdup(daemon_auth_choices + 1);
+		if ((cp = strchr(daemon_auth_choices, '\n')) != NULL)
+			*cp = '\0';
+	}
+
 	if (protocol_version > remote_protocol) {
 		protocol_version = remote_protocol;
 		if (remote_sub)
@@ -429,7 +434,7 @@ static int read_arg_from_pipe(int fd, char *buf, int limit)
 }
 #endif

-static void set_env_str(const char *var, const char *str)
+void set_env_str(const char *var, const char *str)
 {
 #ifdef HAVE_SETENV
 	if (setenv(var, str, 1) < 0)
--- a/compat.c
+++ b/compat.c
@@ -60,13 +60,16 @@ extern char *files_from;
 extern char *filesfrom_host;
 extern const char *checksum_choice;
 extern const char *compress_choice;
+extern char *daemon_auth_choices;
 extern filter_rule_list filter_list;
 extern int need_unsorted_flist;
 #ifdef ICONV_OPTION
 extern iconv_t ic_send, ic_recv;
 extern char *iconv_opt;
 #endif
-extern struct name_num_obj valid_checksums;
+extern struct name_num_obj valid_checksums, valid_auth_checksums;
+
+extern struct name_num_item *xfer_sum_nni;

 int remote_protocol = 0;
 int file_extra_cnt = 0; /* count of file-list extras that everyone gets */
@@ -79,6 +82,9 @@ int inplace_partial = 0;
 int do_negotiated_strings = 0;
 int xmit_id0_names = 0;

+struct name_num_item *xattr_sum_nni;
+int xattr_sum_len = 0;
+
 /* These index values are for the file-list's extra-attribute array. */
 int pathname_ndx, depth_ndx, atimes_ndx, crtimes_ndx, uid_ndx, gid_ndx, acls_ndx, xattrs_ndx, unsort_ndx;

@@ -93,19 +99,19 @@ int filesfrom_convert = 0;

 struct name_num_item valid_compressions_items[] = {
 #ifdef SUPPORT_ZSTD
-	{ CPRES_ZSTD, "zstd", NULL },
+	{ CPRES_ZSTD, 0, "zstd", NULL },
 #endif
 #ifdef SUPPORT_LZ4
-	{ CPRES_LZ4, "lz4", NULL },
+	{ CPRES_LZ4, 0, "lz4", NULL },
 #endif
-	{ CPRES_ZLIBX, "zlibx", NULL },
-	{ CPRES_ZLIB, "zlib", NULL },
-	{ CPRES_NONE, "none", NULL },
-	{ 0, NULL, NULL }
+	{ CPRES_ZLIBX, 0, "zlibx", NULL },
+	{ CPRES_ZLIB, 0, "zlib", NULL },
+	{ CPRES_NONE, 0, "none", NULL },
+	{ 0, 0, NULL, NULL }
 };

 struct name_num_obj valid_compressions = {
-	"compress", NULL, NULL, 0, 0, valid_compressions_items
+	"compress", NULL, 0, 0, valid_compressions_items
 };

 #define CF_INC_RECURSE	 (1<<0)
@@ -127,11 +133,7 @@ static void check_sub_protocol(void)
 {
 	char *dot;
 	int their_protocol, their_sub;
-#if SUBPROTOCOL_VERSION != 0
-	int our_sub = protocol_version < PROTOCOL_VERSION ? 0 : SUBPROTOCOL_VERSION;
-#else
-	int our_sub = 0;
-#endif
+	int our_sub = get_subprotocol_version();

 	/* client_info starts with VER.SUB string if client is a pre-release. */
 	if (!(their_protocol = atoi(client_info))
@@ -178,8 +180,8 @@ void set_allow_inc_recurse(void)

 void parse_compress_choice(int final_call)
 {
-	if (valid_compressions.negotiated_name)
-		do_compression = valid_compressions.negotiated_num;
+	if (valid_compressions.negotiated_nni)
+		do_compression = valid_compressions.negotiated_nni->num;
 	else if (compress_choice) {
 		struct name_num_item *nni = get_nni_by_name(&valid_compressions, compress_choice, -1);
 		if (!nni) {
@@ -201,8 +203,8 @@ void parse_compress_choice(int final_call)
 		compress_choice = NULL;

 	/* Snag the compression name for both write_batch's option output & the following debug output. */
-	if (valid_compressions.negotiated_name)
-		compress_choice = valid_compressions.negotiated_name;
+	if (valid_compressions.negotiated_nni)
+		compress_choice = valid_compressions.negotiated_nni->name;
 	else if (compress_choice == NULL) {
 		struct name_num_item *nni = get_nni_by_num(&valid_compressions, do_compression);
 		compress_choice = nni ? nni->name : "UNKNOWN";
@@ -212,7 +214,7 @@ void parse_compress_choice(int final_call)
 	 && (do_compression != CPRES_NONE || do_compression_level != CLVL_NOT_SPECIFIED)) {
 		rprintf(FINFO, "%s%s compress: %s (level %d)\n",
 			am_server ? "Server" : "Client",
-			valid_compressions.negotiated_name ? " negotiated" : "",
+			valid_compressions.negotiated_nni ? " negotiated" : "",
 			compress_choice, do_compression_level);
 	}
 }
@@ -225,6 +227,8 @@ struct name_num_item *get_nni_by_name(struct name_num_obj *nno, const char *name
 		len = strlen(name);

 	for (nni = nno->list; nni->name; nni++) {
+		if (nni->num == CSUM_gone)
+			continue;
 		if (strncasecmp(name, nni->name, len) == 0 && nni->name[len] == '\0')
 			return nni;
 	}
@@ -259,10 +263,12 @@ static void init_nno_saw(struct name_num_obj *nno, int val)
 	if (!nno->saw) {
 		nno->saw = new_array0(uchar, nno->saw_len);

-		/* We'll take this opportunity to make sure that the main_name values are set right. */
+		/* We'll take this opportunity to set the main_nni values for duplicates. */
 		for (cnt = 1, nni = nno->list; nni->name; nni++, cnt++) {
+			if (nni->num == CSUM_gone)
+				continue;
 			if (nno->saw[nni->num])
-				nni->main_name = nno->list[nno->saw[nni->num]-1].name;
+				nni->main_nni = &nno->list[nno->saw[nni->num]-1];
 			else
 				nno->saw[nni->num] = cnt;
 		}
@@ -288,8 +294,8 @@ static int parse_nni_str(struct name_num_obj *nno, const char *from, char *tobuf
 				struct name_num_item *nni = get_nni_by_name(nno, tok, to - tok);
 				if (nni && !nno->saw[nni->num]) {
 					nno->saw[nni->num] = ++cnt;
-					if (nni->main_name) {
-						to = tok + strlcpy(tok, nni->main_name, tobuf_len - (tok - tobuf));
+					if (nni->main_nni) {
+						to = tok + strlcpy(tok, nni->main_nni->name, tobuf_len - (tok - tobuf));
 						if (to - tobuf >= tobuf_len) {
 							to = tok - 1;
 							break;
@@ -323,13 +329,44 @@ static int parse_nni_str(struct name_num_obj *nno, const char *from, char *tobuf
 	return to - tobuf;
 }

+static int parse_negotiate_str(struct name_num_obj *nno, char *tmpbuf)
+{
+	struct name_num_item *nni, *ret = NULL;
+	int best = nno->saw_len; /* We want best == 1 from the client list, so start with a big number. */
+	char *space, *tok = tmpbuf;
+	while (tok) {
+		while (*tok == ' ') tok++; /* Should be unneeded... */
+		if (!*tok)
+			break;
+		if ((space = strchr(tok, ' ')) != NULL)
+			*space = '\0';
+		nni = get_nni_by_name(nno, tok, -1);
+		if (space) {
+			*space = ' ';
+			tok = space + 1;
+		} else
+			tok = NULL;
+		if (!nni || !nno->saw[nni->num] || best <= nno->saw[nni->num])
+			continue;
+		ret = nni;
+		best = nno->saw[nni->num];
+		if (best == 1 || am_server) /* The server side stops at the first acceptable client choice */
+			break;
+	}
+	if (ret) {
+		free(nno->saw);
+		nno->saw = NULL;
+		nno->negotiated_nni = ret->main_nni ? ret->main_nni : ret;
+		return 1;
+	}
+	return 0;
+}
+
 /* This routine is always called with a tmpbuf of MAX_NSTR_STRLEN length, but the
 * buffer may be pre-populated with a "len" length string to use OR a len of -1
 * to tell us to read a string from the fd. */
 static void recv_negotiate_str(int f_in, struct name_num_obj *nno, char *tmpbuf, int len)
 {
-	struct name_num_item *ret = NULL;
-
 	if (len < 0)
 		len = read_vstring(f_in, tmpbuf, MAX_NSTR_STRLEN);

@@ -340,37 +377,8 @@ static void recv_negotiate_str(int f_in, struct name_num_obj *nno, char *tmpbuf,
 			rprintf(FINFO, "Server %s list (on client): %s\n", nno->type, tmpbuf);
 	}

-	if (len > 0) {
-		struct name_num_item *nni;
-		int best = nno->saw_len; /* We want best == 1 from the client list, so start with a big number. */
-		char *space, *tok = tmpbuf;
-		while (tok) {
-			while (*tok == ' ') tok++; /* Should be unneeded... */
-			if (!*tok)
-				break;
-			if ((space = strchr(tok, ' ')) != NULL)
-				*space = '\0';
-			nni = get_nni_by_name(nno, tok, -1);
-			if (space) {
-				*space = ' ';
-				tok = space + 1;
-			} else
-				tok = NULL;
-			if (!nni || !nno->saw[nni->num] || best <= nno->saw[nni->num])
-				continue;
-			ret = nni;
-			best = nno->saw[nni->num];
-			if (best == 1 || am_server) /* The server side stops at the first acceptable client choice */
-				break;
-		}
-		if (ret) {
-			free(nno->saw);
-			nno->saw = NULL;
-			nno->negotiated_name = ret->main_name ? ret->main_name : ret->name;
-			nno->negotiated_num = ret->num;
-			return;
-		}
-	}
+	if (len > 0 && parse_negotiate_str(nno, tmpbuf))
+		return;

 	if (!am_server || !do_negotiated_strings) {
 		char *cp = tmpbuf;
@@ -466,8 +474,10 @@ int get_default_nno_list(struct name_num_obj *nno, char *to_buf, int to_buf_len,
 	init_nno_saw(nno, 0);

 	for (nni = nno->list, len = 0; nni->name; nni++) {
-		if (nni->main_name) {
-			if (!dup_markup)
+		if (nni->num == CSUM_gone)
+			continue;
+		if (nni->main_nni) {
+			if (!dup_markup || nni->main_nni->num == CSUM_gone)
 				continue;
 			delim = dup_markup;
 		}
@@ -556,7 +566,7 @@ static void negotiate_the_strings(int f_in, int f_out)
 	/* If the other side is too old to negotiate, the above steps just made sure that
 	 * the env didn't disallow the old algorithm. Mark things as non-negotiated. */
 	if (!do_negotiated_strings)
-		valid_checksums.negotiated_name = valid_compressions.negotiated_name = NULL;
+		valid_checksums.negotiated_nni = valid_compressions.negotiated_nni = NULL;
 }

 void setup_protocol(int f_out,int f_in)
@@ -805,11 +815,73 @@ void setup_protocol(int f_out,int f_in)
 		checksum_seed = read_int(f_in);
 	}

-	parse_checksum_choice(1); /* Sets checksum_type & xfersum_type */
+	parse_checksum_choice(1); /* Sets file_sum_nni & xfer_sum_nni */
 	parse_compress_choice(1); /* Sets do_compression */

+	/* TODO in the future allow this algorithm to be chosen somehow, but it can't get too
+	 * long or the size starts to cause a problem in the xattr abbrev/non-abbrev code. */
+	xattr_sum_nni = parse_csum_name(NULL, 0);
+	xattr_sum_len = csum_len_for_type(xattr_sum_nni->num, 0);
+
 	if (write_batch && !am_server)
 		write_batch_shell_file();

 	init_flist();
 }
+
+void output_daemon_greeting(int f_out, int am_client)
+{
+	char tmpbuf[MAX_NSTR_STRLEN];
+	int our_sub = get_subprotocol_version();
+
+	get_default_nno_list(&valid_auth_checksums, tmpbuf, MAX_NSTR_STRLEN, '\0');
+
+	io_printf(f_out, "@RSYNCD: %d.%d %s\n", protocol_version, our_sub, tmpbuf);
+
+	if (am_client && DEBUG_GTE(NSTR, 2))
+		rprintf(FINFO, "Client %s list (on client): %s\n", valid_auth_checksums.type, tmpbuf);
+}
+
+void negotiate_daemon_auth(int f_out, int am_client)
+{
+	char tmpbuf[MAX_NSTR_STRLEN];
+	int save_am_server = am_server;
+	int md4_is_old = 0;
+
+	if (!am_client)
+		am_server = 1;
+
+	if (daemon_auth_choices)
+		strlcpy(tmpbuf, daemon_auth_choices, MAX_NSTR_STRLEN);
+	else {
+		strlcpy(tmpbuf, protocol_version >= 30 ? "md5" : "md4", MAX_NSTR_STRLEN);
+		md4_is_old = 1;
+	}
+
+	if (am_client) {
+		recv_negotiate_str(-1, &valid_auth_checksums, tmpbuf, strlen(tmpbuf));
+		if (DEBUG_GTE(NSTR, 1)) {
+			rprintf(FINFO, "Client negotiated %s: %s\n", valid_auth_checksums.type,
+				valid_auth_checksums.negotiated_nni->name);
+		}
+	} else {
+		if (!parse_negotiate_str(&valid_auth_checksums, tmpbuf)) {
+			get_default_nno_list(&valid_auth_checksums, tmpbuf, MAX_NSTR_STRLEN, '\0');
+			io_printf(f_out, "@ERROR: your client does not support one of our daemon-auth checksums: %s\n",
+				  tmpbuf);
+			exit_cleanup(RERR_UNSUPPORTED);
+		}
+	}
+	am_server = save_am_server;
+	if (md4_is_old && valid_auth_checksums.negotiated_nni->num == CSUM_MD4)
+		valid_auth_checksums.negotiated_nni->num = CSUM_MD4_OLD;
+}
+
+int get_subprotocol_version()
+{
+#if SUBPROTOCOL_VERSION != 0
+	return protocol_version < PROTOCOL_VERSION ? 0 : SUBPROTOCOL_VERSION;
+#else
+	return 0;
+#endif
+}
--- a/configure.ac
+++ b/configure.ac
@@ -136,6 +136,16 @@ if test x"$GCC" = x"yes"; then
 	CFLAGS="$CFLAGS -Wall -W"
 fi

+AC_ARG_WITH(openssl-conf,
+	AS_HELP_STRING([--with-openssl-conf=PATH],[set default OPENSSL_CONF path for rsync]))
+case "$with_openssl_conf" in
+    *[^-/a-zA-Z0-9.,=@+_]*) AC_MSG_ERROR([Invalid path given to --with-openssl-conf]) ;;
+    /*) CFLAGS="$CFLAGS -DSET_OPENSSL_CONF=$with_openssl_conf" ;;
+    no|'') ;;
+    yes) AC_MSG_ERROR([No path given to --with-openssl-conf]) ;;
+    *) AC_MSG_ERROR([Non absolute path given to --with-openssl-conf]) ;;
+esac
+
 AC_ARG_WITH(rrsync,
        AS_HELP_STRING([--with-rrsync],[also install the rrsync script and its manpage]))
 if test x"$with_rrsync" != x"yes"; then
--- a/flist.c
+++ b/flist.c
@@ -33,7 +33,6 @@ extern int am_sender;
 extern int am_generator;
 extern int inc_recurse;
 extern int always_checksum;
-extern int checksum_type;
 extern int module_id;
 extern int ignore_errors;
 extern int numeric_ids;
@@ -80,6 +79,8 @@ extern struct stats stats;
 extern char *filesfrom_host;
 extern char *usermap, *groupmap;

+extern struct name_num_item *file_sum_nni;
+
 extern char curr_dir[MAXPATHLEN];

 extern struct chmod_mode_struct *chmod_modes;
@@ -145,7 +146,8 @@ void init_flist(void)
 		rprintf(FINFO, "FILE_STRUCT_LEN=%d, EXTRA_LEN=%d\n",
 			(int)FILE_STRUCT_LEN, (int)EXTRA_LEN);
 	}
-	flist_csum_len = csum_len_for_type(checksum_type, 1);
+	/* Note that this isn't identical to file_sum_len in the case of CSUM_MD4_ARCHAIC: */
+	flist_csum_len = csum_len_for_type(file_sum_nni->num, 1);

 	show_filelist_progress = INFO_GTE(FLIST, 1) && xfer_dirs && !am_server && !inc_recurse;
 }
--- a/lib/md-defines.h
+++ b/lib/md-defines.h
@@ -6,6 +6,7 @@

 #define CSUM_CHUNK 64

+#define CSUM_gone -1
 #define CSUM_NONE 0
 #define CSUM_MD4_ARCHAIC 1
 #define CSUM_MD4_BUSTED 2
--- a/lib/md5.c
+++ b/lib/md5.c
@@ -20,7 +20,6 @@

 #include "rsync.h"

-#if !defined USE_OPENSSL || USE_MD5_ASM /* { */
 void md5_begin(md_context *ctx)
 {
 	ctx->A = 0x67452301;
@@ -224,7 +223,6 @@ void md5_result(md_context *ctx, uchar digest[MD5_DIGEST_LEN])
 	SIVALu(digest, 8, ctx->C);
 	SIVALu(digest, 12, ctx->D);
 }
-#endif /* } */

 #ifdef TEST_MD5 /* { */

--- a/lib/mdigest.h
+++ b/lib/mdigest.h
@@ -1,8 +1,7 @@
 /* The include file for both the MD4 and MD5 routines. */

 #ifdef USE_OPENSSL
-#include "openssl/md4.h"
-#include "openssl/md5.h"
+#include <openssl/evp.h>
 #endif
 #include "md-defines.h"

@@ -17,14 +16,6 @@ void mdfour_begin(md_context *md);
 void mdfour_update(md_context *md, const uchar *in, uint32 length);
 void mdfour_result(md_context *md, uchar digest[MD4_DIGEST_LEN]);

-#if defined USE_OPENSSL && !defined USE_MD5_ASM
-#define md5_context MD5_CTX
-#define md5_begin MD5_Init
-#define md5_update MD5_Update
-#define md5_result(cptr, digest) MD5_Final(digest, cptr)
-#else
-#define md5_context md_context
 void md5_begin(md_context *ctx);
 void md5_update(md_context *ctx, const uchar *input, uint32 length);
 void md5_result(md_context *ctx, uchar digest[MD5_DIGEST_LEN]);
-#endif
--- a/log.c
+++ b/log.c
@@ -36,8 +36,6 @@ extern int protocol_version;
 extern int always_checksum;
 extern int preserve_mtimes;
 extern int msgs2stderr;
-extern int xfersum_type;
-extern int checksum_type;
 extern int stdout_format_has_i;
 extern int stdout_format_has_o_or_i;
 extern int logfile_format_has_i;
@@ -62,6 +60,8 @@ extern unsigned int module_dirlen;
 extern char sender_file_sum[MAX_DIGEST_LEN];
 extern const char undetermined_hostname[];

+extern struct name_num_item *xfer_sum_nni, *file_sum_nni;
+
 static int log_initialised;
 static int logfile_was_closed;
 static FILE *logfile_fp;
@@ -680,12 +680,12 @@ static void log_formatted(enum logcode code, const char *format, const char *op,
 			n = NULL;
 			if (S_ISREG(file->mode)) {
 				if (always_checksum)
-					n = sum_as_hex(checksum_type, F_SUM(file), 1);
+					n = sum_as_hex(file_sum_nni->num, F_SUM(file), 1);
 				else if (iflags & ITEM_TRANSFER)
-					n = sum_as_hex(xfersum_type, sender_file_sum, 0);
+					n = sum_as_hex(xfer_sum_nni->num, sender_file_sum, 0);
 			}
 			if (!n) {
-				int sum_len = csum_len_for_type(always_checksum ? checksum_type : xfersum_type,
+				int sum_len = csum_len_for_type(always_checksum ? file_sum_nni->num : xfer_sum_nni->num,
 								always_checksum);
 				memset(buf2, ' ', sum_len*2);
 				buf2[sum_len*2] = '\0';
--- a/main.c
+++ b/main.c
@@ -1743,6 +1743,17 @@ int main(int argc,char *argv[])

 	unset_env_var("DISPLAY");

+#if defined USE_OPENSSL && defined SET_OPENSSL_CONF
+#define TO_STR2(x) #x
+#define TO_STR(x) TO_STR2(x)
+	/* ./configure --with-openssl-conf=/etc/ssl/openssl-rsync.cnf
+	 * defines SET_OPENSSL_CONF as that unquoted pathname. */
+	if (!getenv("OPENSSL_CONF")) /* Don't override it if it's already set. */
+		set_env_str("OPENSSL_CONF", TO_STR(SET_OPENSSL_CONF));
+#undef TO_STR
+#undef TO_STR2
+#endif
+
 	memset(&stats, 0, sizeof(stats));

 	/* Even a non-daemon runs needs the default config values to be set, e.g.
--- a/match.c
+++ b/match.c
@@ -24,7 +24,9 @@

 extern int checksum_seed;
 extern int append_mode;
-extern int xfersum_type;
+
+extern struct name_num_item *xfer_sum_nni;
+extern int xfer_sum_len;

 int updating_basis_file;
 char sender_file_sum[MAX_DIGEST_LEN];
@@ -356,15 +358,13 @@ static void hash_search(int f,struct sum_struct *s,
 **/
 void match_sums(int f, struct sum_struct *s, struct map_struct *buf, OFF_T len)
 {
-	int sum_len;
-
 	last_match = 0;
 	false_alarms = 0;
 	hash_hits = 0;
 	matches = 0;
 	data_transfer = 0;

-	sum_init(xfersum_type, checksum_seed);
+	sum_init(xfer_sum_nni, checksum_seed);

 	if (append_mode > 0) {
 		if (append_mode == 2) {
@@ -405,22 +405,22 @@ void match_sums(int f, struct sum_struct *s, struct map_struct *buf, OFF_T len)
 		matched(f, s, buf, len, -1);
 	}

-	sum_len = sum_end(sender_file_sum);
+	sum_end(sender_file_sum);

 	/* If we had a read error, send a bad checksum.  We use all bits
 	 * off as long as the checksum doesn't happen to be that, in
 	 * which case we turn the last 0 bit into a 1. */
 	if (buf && buf->status != 0) {
 		int i;
-		for (i = 0; i < sum_len && sender_file_sum[i] == 0; i++) {}
-		memset(sender_file_sum, 0, sum_len);
-		if (i == sum_len)
+		for (i = 0; i < xfer_sum_len && sender_file_sum[i] == 0; i++) {}
+		memset(sender_file_sum, 0, xfer_sum_len);
+		if (i == xfer_sum_len)
 			sender_file_sum[i-1]++;
 	}

 	if (DEBUG_GTE(DELTASUM, 2))
 		rprintf(FINFO,"sending file_sum\n");
-	write_buf(f, sender_file_sum, sum_len);
+	write_buf(f, sender_file_sum, xfer_sum_len);

 	if (DEBUG_GTE(DELTASUM, 2)) {
 		rprintf(FINFO, "false_alarms=%d hash_hits=%d matches=%d\n",
--- a/packaging/openssl-rsync.cnf
+++ b/packaging/openssl-rsync.cnf
@@ -0,0 +1,18 @@
+# This config file can be used with rsync to enable legacy digests
+# (such as MD4) by using the OPENSSL_CONF environment variable.
+# See rsync's configure --with-openssl-conf=/path/name option.
+
+openssl_conf = openssl_init
+
+[openssl_init]
+providers = provider_sect
+
+[provider_sect]
+default = default_sect
+legacy = legacy_sect
+
+[default_sect]
+activate = 1
+
+[legacy_sect]
+activate = 1
--- a/receiver.c
+++ b/receiver.c
@@ -56,7 +56,6 @@ extern int inplace;
 extern int inplace_partial;
 extern int allowed_lull;
 extern int delay_updates;
-extern int xfersum_type;
 extern BOOL want_progress_now;
 extern mode_t orig_umask;
 extern struct stats stats;
@@ -68,6 +67,9 @@ extern struct file_list *cur_flist, *first_flist, *dir_flist;
 extern filter_rule_list daemon_filter_list;
 extern OFF_T preallocated_len;

+extern struct name_num_item *xfer_sum_nni;
+extern int xfer_sum_len;
+
 static struct bitbag *delayed_bits = NULL;
 static int phase = 0, redoing = 0;
 static flist_ndx_list batch_redo_list;
@@ -240,7 +242,6 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 	static char file_sum1[MAX_DIGEST_LEN];
 	struct map_struct *mapbuf;
 	struct sum_struct sum;
-	int sum_len;
 	int32 len;
 	OFF_T total_size = F_LENGTH(file);
 	OFF_T offset = 0;
@@ -280,7 +281,7 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 	} else
 		mapbuf = NULL;

-	sum_init(xfersum_type, checksum_seed);
+	sum_init(xfer_sum_nni, checksum_seed);

 	if (append_mode > 0) {
 		OFF_T j;
@@ -393,7 +394,7 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 	if (INFO_GTE(PROGRESS, 1))
 		end_progress(total_size);

-	sum_len = sum_end(file_sum1);
+	sum_end(file_sum1);

 	if (do_fsync && fd != -1 && fsync(fd) != 0) {
 		rsyserr(FERROR, errno, "fsync failed on %s", full_fname(fname));
@@ -403,10 +404,10 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 	if (mapbuf)
 		unmap_file(mapbuf);

-	read_buf(f_in, sender_file_sum, sum_len);
+	read_buf(f_in, sender_file_sum, xfer_sum_len);
 	if (DEBUG_GTE(DELTASUM, 2))
 		rprintf(FINFO,"got file_sum\n");
-	if (fd != -1 && memcmp(file_sum1, sender_file_sum, sum_len) != 0)
+	if (fd != -1 && memcmp(file_sum1, sender_file_sum, xfer_sum_len) != 0)
 		return 0;
 	return 1;
 }
--- a/rsync.h
+++ b/rsync.h
@@ -826,6 +826,7 @@ extern int uid_ndx;
 extern int gid_ndx;
 extern int acls_ndx;
 extern int xattrs_ndx;
+extern int file_sum_len;

 #ifdef USE_FLEXIBLE_ARRAY
 #define FILE_STRUCT_LEN (sizeof (struct file_struct))
@@ -836,7 +837,7 @@ extern int xattrs_ndx;
 #define DEV_EXTRA_CNT 2
 #define DIRNODE_EXTRA_CNT 3
 #define EXTRA64_CNT ((sizeof (union file_extras64) + EXTRA_LEN - 1) / EXTRA_LEN)
-#define SUM_EXTRA_CNT ((MAX_DIGEST_LEN + EXTRA_LEN - 1) / EXTRA_LEN)
+#define SUM_EXTRA_CNT ((file_sum_len + EXTRA_LEN - 1) / EXTRA_LEN)

 #define REQ_EXTRA(f,ndx) ((union file_extras*)(f) - (ndx))
 #define OPT_EXTRA(f,bump) ((union file_extras*)(f) - file_extra_cnt - 1 - (bump))
@@ -1162,16 +1163,16 @@ typedef struct {
 #define NSTR_COMPRESS 1

 struct name_num_item {
-	int num;
-	const char *name, *main_name;
+	int num, flags;
+	const char *name;
+	struct name_num_item *main_nni;
 };

 struct name_num_obj {
 	const char *type;
-	const char *negotiated_name;
+	struct name_num_item *negotiated_nni;
 	uchar *saw;
 	int saw_len;
-	int negotiated_num;
 	struct name_num_item *list;
 };

--- a/usage.c
+++ b/usage.c
@@ -23,8 +23,7 @@
 #include "git-version.h"
 #include "default-cvsignore.h"

-extern struct name_num_obj valid_checksums;
-extern struct name_num_obj valid_compressions;
+extern struct name_num_obj valid_checksums, valid_compressions, valid_auth_checksums;

 static char *istring(const char *fmt, int val)
 {
@@ -205,6 +204,10 @@ void print_rsync_version(enum logcode f)
 	get_default_nno_list(&valid_compressions, tmpbuf, sizeof tmpbuf, '(');
 	rprintf(f, "    %s\n", tmpbuf);

+	rprintf(f, "Daemon auth list:\n");
+	get_default_nno_list(&valid_auth_checksums, tmpbuf, sizeof tmpbuf, '(');
+	rprintf(f, "    %s\n", tmpbuf);
+
 #ifdef MAINTAINER_MODE
 	rprintf(f, "Panic Action: \"%s\"\n", get_panic_action());
 #endif
--- a/xattrs.c
+++ b/xattrs.c
@@ -39,9 +39,13 @@ extern int preserve_specials;
 extern int checksum_seed;
 extern int saw_xattr_filter;

+extern struct name_num_item *xattr_sum_nni;
+extern int xattr_sum_len;
+
 #define RSYNC_XAL_INITIAL 5
 #define RSYNC_XAL_LIST_INITIAL 100

+#define MAX_XATTR_DIGEST_LEN MD5_DIGEST_LEN
 #define MAX_FULL_DATUM 32

 #define HAS_PREFIX(str, prfx) (*(str) == *(prfx) && strncmp(str, prfx, sizeof (prfx) - 1) == 0)
@@ -269,8 +273,8 @@ static int rsync_xal_get(const char *fname, item_list *xalp)

 		if (datum_len > MAX_FULL_DATUM) {
 			/* For large datums, we store a flag and a checksum. */
-			name_offset = 1 + MAX_DIGEST_LEN;
-			sum_init(-1, checksum_seed);
+			name_offset = 1 + MAX_XATTR_DIGEST_LEN;
+			sum_init(xattr_sum_nni, checksum_seed);
 			sum_update(ptr, datum_len);
 			free(ptr);

@@ -382,7 +386,7 @@ static int64 xattr_lookup_hash(const item_list *xalp)
 	for (i = 0; i < xalp->count; i++) {
 		key += hashlittle(rxas[i].name, rxas[i].name_len);
 		if (rxas[i].datum_len > MAX_FULL_DATUM)
-			key += hashlittle(rxas[i].datum, MAX_DIGEST_LEN);
+			key += hashlittle(rxas[i].datum, xattr_sum_len);
 		else
 			key += hashlittle(rxas[i].datum, rxas[i].datum_len);
 	}
@@ -435,7 +439,7 @@ static int find_matching_xattr(const item_list *xalp)
 			if (rxas1[j].datum_len > MAX_FULL_DATUM) {
 				if (memcmp(rxas1[j].datum + 1,
 					   rxas2[j].datum + 1,
-					   MAX_DIGEST_LEN) != 0)
+					   xattr_sum_len) != 0)
 					break;
 			} else {
 				if (memcmp(rxas1[j].datum, rxas2[j].datum,
@@ -535,7 +539,7 @@ int send_xattr(int f, stat_x *sxp)
 #endif
 			write_buf(f, name, name_len);
 			if (rxa->datum_len > MAX_FULL_DATUM)
-				write_buf(f, rxa->datum + 1, MAX_DIGEST_LEN);
+				write_buf(f, rxa->datum + 1, xattr_sum_len);
 			else
 				write_bigbuf(f, rxa->datum, rxa->datum_len);
 		}
@@ -588,7 +592,7 @@ int xattr_diff(struct file_struct *file, stat_x *sxp, int find_all)
 		else if (snd_rxa->datum_len > MAX_FULL_DATUM) {
 			same = cmp == 0 && snd_rxa->datum_len == rec_rxa->datum_len
 			    && memcmp(snd_rxa->datum + 1, rec_rxa->datum + 1,
-				      MAX_DIGEST_LEN) == 0;
+				      xattr_sum_len) == 0;
 			/* Flag unrequested items that we need. */
 			if (!same && find_all && snd_rxa->datum[0] == XSTATE_ABBREV)
 				snd_rxa->datum[0] = XSTATE_TODO;
@@ -797,7 +801,7 @@ void receive_xattr(int f, struct file_struct *file)
 		rsync_xa *rxa;
 		size_t name_len = read_varint(f);
 		size_t datum_len = read_varint(f);
-		size_t dget_len = datum_len > MAX_FULL_DATUM ? 1 + MAX_DIGEST_LEN : datum_len;
+		size_t dget_len = datum_len > MAX_FULL_DATUM ? 1 + (size_t)xattr_sum_len : datum_len;
 		size_t extra_len = MIGHT_NEED_RPRE ? RPRE_LEN : 0;
 		if (SIZE_MAX - dget_len < extra_len || SIZE_MAX - dget_len - extra_len < name_len)
 			overflow_exit("receive_xattr");
@@ -812,7 +816,7 @@ void receive_xattr(int f, struct file_struct *file)
 			read_buf(f, ptr, dget_len);
 		else {
 			*ptr = XSTATE_ABBREV;
-			read_buf(f, ptr + 1, MAX_DIGEST_LEN);
+			read_buf(f, ptr + 1, xattr_sum_len);
 		}

 		if (saw_xattr_filter) {
@@ -943,7 +947,7 @@ static int rsync_xal_set(const char *fname, item_list *xalp,
 	rsync_xa *rxas = xalp->items;
 	ssize_t list_len;
 	size_t i, len;
-	char *name, *ptr, sum[MAX_DIGEST_LEN];
+	char *name, *ptr, sum[MAX_XATTR_DIGEST_LEN];
 #ifdef HAVE_LINUX_XATTRS
 	int user_only = am_root <= 0;
 #endif
@@ -958,7 +962,6 @@ static int rsync_xal_set(const char *fname, item_list *xalp,
 		name = rxas[i].name;

 		if (XATTR_ABBREV(rxas[i])) {
-			int sum_len;
 			/* See if the fnamecmp version is identical. */
 			len = name_len = rxas[i].name_len;
 			if ((ptr = get_xattr_data(fnamecmp, name, &len, 1)) == NULL) {
@@ -975,10 +978,10 @@ static int rsync_xal_set(const char *fname, item_list *xalp,
 				goto still_abbrev;
 			}

-			sum_init(-1, checksum_seed);
+			sum_init(xattr_sum_nni, checksum_seed);
 			sum_update(ptr, len);
-			sum_len = sum_end(sum);
-			if (memcmp(sum, rxas[i].datum + 1, sum_len) != 0) {
+			sum_end(sum);
+			if (memcmp(sum, rxas[i].datum + 1, xattr_sum_len) != 0) {
 				free(ptr);
 				goto still_abbrev;
 			}