[openssl-users] Fixed-size digest using EVP with algos ECDSA+SHA256

Daniel Andrade daniel.andrade at tecnico.ulisboa.pt
Mon Aug 7 19:08:07 UTC 2017

Hi all,

I'm writing functions to create a digest of a data buffer using 
ECDSA+SHA256. I've been trying to work with only the high-level EVP 
interface, and not use the low-level interfaces.

My understanding is that the resulting digest is an ASN.1 structure. I 
have to feed this digest to the Intel SGX runtime, which requires a 
fixed-size input (they actually have two separates arrays, one for X and 
one for Y, each with 32-byte length).

Is it possible to get a fixed-sized digest using ECDSA/SHA256, I mean 
does OpenSSL have functions for this? Or could someone give me some 
pointers on how to proceed to convert that result to the 64-byte fixed size?


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