Hello,
I am using EVP to encrypt and decrypt some files. This works pretty
well. But now I restructured my code in order to be able to decrypt data
streams so I don't have to save an unencrypted version of a file on the
hd before computing it. To do that I initialize the cipher context
before the use of data streams and use the same one until all streams
are done. According to the notes regarding EVP_CipherFinal_ex() this is
okay ("... because they can reuse an existing context without allocating
and freeing it up on each call").
A stream data package can be a whole file or just parts of an encrypted
file and is divided into chunks that are multiples of 32. As the last
chunk can be less than 32 bytes padding is enabled. Now my problem is
that EVP_CipherFinal_ex, which is called when a stream data package is
done, fails with the following error:
error:06065064:lib(6):func(101):reason(100):.\crypto\evp\evp_enc.c:467
or 474
There are a few observations I made that seem strange to me:
- If I disable padding I don't get any errors but data seems to
be missing.
- If padding is enabled I get the above described error but no
data seems to be missing.
- Even if the data chunk is a multiple of 32 bytes
EVP_DecryptUpdate() copies a block of data to "ctx->final" and sets
"ctx->final_used" as true because "ctx->buf_len" equals 0
The general structure of my code looks like this:
InitCipherContext()
For each stream data package do
While(dataChunk)
EVP_CipherUpdate(dataChunk)
EndWhile
EVP_CipherFinal_ex()
EndFor
ClearCipherContext()
Does anyone have any idea what might be the problem here?
Thanks a lot for your help.
Cheers
Nico
