Stephen,
Thanks for your solution.
Well I'd add the BIG disclaimer that will NOT work in future when OpenSSL
structures are made opaque and almost certainly will fail if you have an
ENGINE.
Understood. I am new to openssl and I am reading up about 'ENGINE's in
openssl. When you say it will fail when there is an 'ENGINE', do you mean if
I use EVP_DIGEST functions (from the example on openssl.org), your solution
will not work? If yes, is the solution as simple as using SHA1_Init,
SHA1_Update, SHA1_Final functions instead?
What you need to do is copy the md_ctx-data (which will be a flat buffer
for
the software SHA1 implementation) for md_ctx-digest-md_size bytes. Save
that
somewhere and after calling init the second time copy it back. Do NOT try
restoring the context with different versions of OpenSSL or different
architectures.
Will this work with plain old SHA also? I will try to find the answers for
some of the questions on my own by writing some code. But any help from your
side will be much appreciated.
Subra
