- Increased file name IV length

main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/AesCryptographicConfiguration.java

@@ -78,9 +78,10 @@ interface AesCryptographicConfiguration {
 
 	/**
 	 * Number of non-zero bytes in the IV used for file name encryption. Less means shorter encrypted filenames, more means higher entropy.
-	 * Maximum length is {@value #AES_BLOCK_LENGTH}.
+	 * Maximum length is {@value #AES_BLOCK_LENGTH}. Even the shortest base32 (see {@link FileNamingConventions#ENCRYPTED_FILENAME_CODEC})
+	 * encoded byte array will need 8 chars. The maximum number of bytes that fit in 8 base32 chars is 5. Thus 5 is the ideal length.
 	 */
-	int FILE_NAME_IV_LENGTH = 4;
+	int FILE_NAME_IV_LENGTH = 5;
 
 	/**
 	 * Number of iterations for key derived from user pw. High iteration count for better resistance to bruteforcing.

main/crypto-aes/src/main/java/org/cryptomator/crypto/aes256/FileNamingConventions.java

@@ -22,7 +22,7 @@ interface FileNamingConventions {
 	String MASTERKEY_FILE_EXT = ".masterkey.json";
 
 	/**
-	 * How to encode the encrypted file names safely.
+	 * How to encode the encrypted file names safely. Base32 uses only alphanumeric characters and is case-insensitive.
 	 */
 	BaseNCodec ENCRYPTED_FILENAME_CODEC = new Base32();