CODEWITHSUNDEEP
copensslcryptographyshasha512
Umayr
Umayr

Reputation: 933

How to calculate SHA512/224 and SHA512/256 hashes using OpenSSL?

Here's how I calculate a SHA512 hash in C.

#include <openssl/sha.h>
#include <stdio.h>

char *calc_sha512(char *data) {
    SHA512_CTX ctx;
    char *md = malloc(sizeof(char)*(SHA512_DIGEST_LENGTH+1));

    SHA512_Init(&ctx);
    SHA512_Update(&ctx, data, strlen(data));
    SHA512_Final(md, &ctx);
    md[SHA512_DIGEST_LENGTH] = '\0';

    return md;
}

int main() {
    printf("%s\n", calc_sha512("foo"));

    return 1;
}

Now when I try to transform it to 512/t (either 512/224 or 512/256), it doesn't work. I initially thought that for calculating a 512/t hash, you'd simply have to truncate the output to t bits, but upon further reading, it doesn't only truncate the output, it also have different initial constant values. So I'm trying to figure out any function in OpenSSL that supports that? So far I have looked into docs and header files, I can't find such method under either SHA or EVP. Does OpenSSL even support SHA512/t hashing algorithms? Does it provide the functionality out of the box? Any pointers to that would be helpful.

Upvotes: 2

Views: 3472

Answers (2)

Arthur H
Arthur H

Reputation: 191

this function should return the SHA512/256 hash (binary form, not printable)

char *calc_sha512_256(char *data, unsigned int data_len) {
    char *hash = malloc(SHA256_DIGEST_LENGTH);

    if (!EVP_Digest(data, data_len, hash, NULL, EVP_sha512_256(), NULL)) {
        free(hash);
        hash = NULL;
    }
    return hash;
}

Upvotes: 0

wvh
wvh

Reputation: 191

As you noticed, those truncated sha512 hashes use different initalisation vectors, probably to avoid giving away part of the actual sha512 hash if they would just literally truncate those bytes.

Support for sha512_256 has been implemented in the OpenSSL master tree a few months ago and will likely be in OpenSSL 1.1.1.

Check the changelog: https://www.openssl.org/news/changelog.txt

Or the commit on Github: https://github.com/openssl/openssl/commit/4bed94f0c11ef63587c6b2edb03c3c438e221604

... so depending on the platform you're on, you could use those new functions in the near future just like you are doing with the sha512 example you provided.

Upvotes: 0

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