This class implements a KeyGenerator for the PBKDF2 (password-based-key-derivation-function-2) specified by the PKCS#5 v2.1 Password-Based Cryptography Standard to derive a key from a password. The PBKDF2 key derivation function PBKDF2 needs the following parameters: salt value, iteration count, length of the to-be-derived key, and (MAC based) pseudo random function (default: HMCA/SHA1).

06-21-2018, 01:05 PM (This post was last modified: 06-21-2018, 01:06 PM by MihaZupan.)

Pkcs5_pbkdf2_hmac_sha1 Source Code

Hello everyone!
Diving into the Telegram Desktop source code I was able to write a program that decrypts and parses the local storage.
One option the client provides is to set a passcode - any string of any length - that is optionally used to encrypt a part of said local storage.
Testing whether the passcode is valid is a multi-step process (shortened for clarity):
1. Read the salt (32 bytes), encrypted data and sha1 of decrypted data from a file.
2. Compute a PKCS5_PBKDF2_HMAC_SHA1 on the UTF8(passcode), using the salt, 4000 iterations, keysize of 256 bytes
3. Use a Telegram-specific KDF to get the AesKey and AesIV (Relatively cheap - bunch of memcpy and 4x sha1)
4. Perform an AES-IGE-DECRYPT on the encrypted data using the derived key and IV from step 3.
5. Compare sha1 of decrypted data with the sha1 read in step 1. If they match - passcode is correct.
Using OpenSSL I am able to test around 100 passcodes/s on a Ryzen 1700. That is a sad number.
The obvious time-hog in this process is the 4000 iterations on the PKCS5_PBKDF2_HMAC_SHA1.
Judging from the benchmarks (that use 1000 iterations as far as I'm aware) I estimate that I could achieve a few MH/s using a GPU powered approach.
Since the process is probably too complex to be added as a whole is it possible to use hashcat (or other programs that I am unaware of) to compute the PKCS5_PBKDF2_HMAC_SHA1 keys with the mentioned parameters and pipe generated passcode-key pairs into another program that then validates the keys?
Thank you in advance,
Miha Zupan

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Pkcs5_pbkdf2_hmac_sha1 Source Code

PKCS5_PBKDF2_HMAC() derives a key from a password using a salt and iteration count as specified in RFC 2898.


pass is the password used in the derivation of length passlen. pass is an optional parameter and can be NULL. If passlen is -1, then the function will calculate the length of pass using strlen(3).

salt is the salt used in the derivation of length saltlen. If the salt is NULL, then saltlen must be 0. The function will not attempt to calculate the length of the salt because it is not assumed to be NUL terminated.

iter is the iteration count and its value should be greater than or equal to 1. RFC 2898 suggests an iteration count of at least 1000. Any iter less than 1 is treated as a single iteration.

digest is the message digest function used in the derivation. Values include any of the EVP_* message digests. PKCS5_PBKDF2_HMAC_SHA1() calls PKCS5_PBKDF2_HMAC() with EVP_sha1(3).

Man Pkcs5_pbkdf2_hmac_sha1


The derived key will be written to out. The size of the out buffer is specified via keylen.

Pkcs5_pbkdf2_hmac_sha1 Online

A typical application of this function is to derive keying material for an encryption algorithm from a password in the pass, a salt in salt, and an iteration count.

Pkcs5_pbkdf2_hmac_sha1 Java

Increasing the iter parameter slows down the algorithm which makes it harder for an attacker to perform a brute force attack using a large number of candidate passwords.