Lorenzo wrote: > I have a quick question to ask. I'm using the EVP_EncryptInit and > EVP_DecryptInit functions to stream data to a file. Basically, I > encrypt data , one byte at a time, which is in the put area of my > filebuf object and send it out. I When I get data from the file, I > decrypt each byte I receive one byte at a time. The problem is when i > use 'seekg(x)' to seek to a point in the file , when I try to decrypt > the buffer I get back, the results are wrong. However, when I start > from the beginning, every thing is fine. When I seek, it does seek to > the right byte in the file. Does any one know why this may be the case? > Ecryption does (usually) not encrypt each byte independently from all the others. The encryption of a byte in the stream depends on what was done before. So, seeking to a different position in the file gets the encryption routines out of sync and you get garbage. You have to read all data.... If you want your applicatoin to use a seek command, have a look at the BIOs in OpenSSL (an abstraction of I/O-Operations). BIOs can be layered and perform some kind of filtering (e.g. RC4 encryption/decryption). And they provide a BIO_seek() command. I havn't tried it myself, but I assume it does the right stuff.
Jörg ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List [EMAIL PROTECTED] Automated List Manager [EMAIL PROTECTED]
