On Wed, Apr 01, 2009, m r wrote: > I'm looking to migrate AES encryption code from BSAFE to openSSL. As a test, > I encrypted a string using BSAFE AES & tried to decrypt using AES of > openSSL. The openSSL manages to decrypt, but it adds some junk (mostly > unprintable characters) in the end. For example, if my input is 1234, the > decrypted output in hex form is [313233340c0c0c0c0c0c0c0c0c0c0c0c], > (31323334 is 1234 in hex form). > For 12345 -> [31323334350b0b0b0b0b0b0b0b0b0b0b] > For 123456 -> [3132333435360a0a0a0a0a0a0a0a0a0a] > > Basically, the junk after the decrypted text is 16 - (string length of > decrypted text) > > For example, 1234's length is 4, 16 - 4 = 12 = 0c in hex & so it gets > filled with that. (313233340c0c0c0c0c0c0c0c0c0c0c0c) > For example, 12345's length is 5, 16 - 5 = 11 = 0b in hex & so it gets > filled with that.(31323334350b0b0b0b0b0b0b0b0b0b0b) > > So what needs to be done to prevent openSSL API [I'm > using AES_cbc_encrypt()] to prevent it from writing this strange junk at the > end? >
Block ciphers can only encrypt a multiple of the block length which for AES is 16 bytes. Padding is added to ubambiguously represent the true length. The standard OpenSSL EVP routines (see manual pages) automatically remove this padding (which BSAFE is adding, not OpenSSL) whereas the low level AES routines decrypt the raw data including padding. Steve. -- Dr Stephen N. Henson. Email, S/MIME and PGP keys: see homepage OpenSSL project core developer and freelance consultant. Homepage: http://www.drh-consultancy.demon.co.uk ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
