X-Git-Url: http://git.claws-mail.org/?p=claws.git;a=blobdiff_plain;f=doc%2Fsrc%2Fpassword_encryption.txt;h=f618378d3e2349e8b277053f7bcfa8d3f1e0c0ae;hp=50873dc35466ba8e423b82f00c1a168f6954a74f;hb=a7f0d049b6a7f1df5fe4e6487ddbb140c22370e0;hpb=54ce0e858a8a8afb81cf1e0302b39b1f9be4b0d0

diff --git a/doc/src/password_encryption.txt b/doc/src/password_encryption.txt
index 50873dc35..f618378d3 100644
--- a/doc/src/password_encryption.txt
+++ b/doc/src/password_encryption.txt
@@ -4,21 +4,35 @@ stored encrypted using AES-256-CBC, using following scheme:
 
 Encryption/decryption key is derived from either PASSCRYPT_KEY, or
 user-selected master passphrase, using PBKDF2, using salt from
-'master_passphrase_salt'.
+'master_passphrase_salt', and number of rounds (iterations) from
+'master_passphrase_pbkdf2_rounds'.
 
-IV for the cipher is filled with random bytes.
+IV (initialization vector) for the cipher is filled with random bytes.
 
 
 Encryption
 ----------
-We prepare a buffer 128+blocksize bytes long, with one block of random
-data at the beginning, followed by the password we want to encrypt,
-rest is padded with zero bytes.
-
-We encrypt the buffer.
+We prepare a buffer long enough to fit the NULL-terminated password string
+plus one cipher block in it, with one block of random data at the beginning,
+followed by the password we want to encrypt (in UTF-8), rest is padded
+with zero bytes.
+
+The minimal buffer size is 128+blocksize, and if the password (including
+the trailing NULL byte) is longer than 128 bytes, the size is increased by
+another 128 bytes until it is long enough to fit the password plus one
+cipher block. This is to make it harder to guess the password length from
+length of the encrypted string. So for example, if the password (again,
+including the trailing NULL byte) is 129 characters long, our buffer will
+be 256+blocksize bytes long.
+
+We encrypt the buffer using the encryption key and IV mentioned above,
+resulting in ciphertext of the same length as the buffer.
 
 We base64-encode the ciphertext, and store it as:
-"{algorithm}encodedciphertext"
+"{algorithm,rounds}encodedciphertext"
+
+"rounds" is an integer value set to number of PBKDF2 rounds used to
+generate the key derivation used as encryption key.
 
 
 Decryption
@@ -26,10 +40,11 @@ Decryption
 We strip the "{algorithm}" (after verifying that it matches what we
 expect) and base64-decode the remaining ciphertext.
 
-We decrypt the ciphertext.
+We decrypt the ciphertext using decryption key and IV mentioned above,
+resulting in plaintext of the same length as the ciphertext.
 
-We discard the first block, and the rest is a zero-terminated string
-with our password.
+We discard the first block from plaintext, and the rest is a
+zero-terminated string with our password in UTF-8.
 
 
 Why the random block at the beginning?