>From: owner-openssl-us...@openssl.org On Behalf Of scott...@csweber.com >Sent: Friday, 11 May, 2012 17:09
>I manually padded the input in the C code with spaces. Then I >manually padded the input file with spaces. Now both cleartexts >are exactly 16 bytes long. >The output from the openssl executable is now 32 bytes...? >Where did it decide to do that? >So, what do I decide how to pad? How far out do I pad it? The padding most cryptography uses and openssl commandline (and EVP_*) does is NOT spaces, it is a count of unused octets repeated. It was popularized by PKCS#5, see RFC 2898 6.1.1-2. Because the padding is always nonempty to avoid ambiguity, if the cleartext is an exact multiple of the blocksize, padding adds an extra block (and unpadding removes it). Marek showed you an example, although it's ambiguous because by coincidence his last plaintext byte was 0a (newline) and his padding bytes were also 0a (16-6=10). When you call AES_* (or DES_* etc) directly, you must add the padding on encrypt and remove it on decrypt yourself. ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
