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Fix KEY_LENGTH for PBKDF2 by specifying it in bits rather than bytes #127
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The KEY_LENGTH constant defined in the KDF.java file is set to 32, in order to stretch the user-supplied password into a 32 byte hash (256 bits) that can be used as the secret key for the ChaCha20 encryption algorithm.
However, with the current code, the PBKDF2_HMAC_SHA256 function only returns a 4 byte hash on line 43.
So, it seems that this function (but not SCRYPT and BCRYPT) requires the key length to be specified in bits rather than bytes, although this fact is not documented anywhere.
I don't think the "case PBKDF2_HMAC_SHA256" block has actually ever been tested before in context, because the ChaCha20 algorithm immediately returns an error if it is not provided with a 256 bits key.
By multiplying the KEY_LENGTH with 8, the PBKDF2_HMAC_SHA256 function returns a 256 bit key, as required, and the hash value is also identical to the one produced by the Python-implementation of Crypt4GH.