Question

The Security services API doesn’t appear to allow me to compute a hash directly. There are plenty of public domain and liberally licensed versions available, but I’d rather use a system library implementation if possible.

The data is accessible via NSData, or plain pointers.

The cryptographic strength of the hash is important to me. SHA-256 is the minimum acceptable hash size.

Answer 1

This is what I’m using for SHA1:

#import <CommonCrypto/CommonDigest.h>

+ (NSData *)sha1:(NSData *)data {
    unsigned char hash[CC_SHA1_DIGEST_LENGTH];
    if ( CC_SHA1([data bytes], [data length], hash) ) {
        NSData *sha1 = [NSData dataWithBytes:hash length:CC_SHA1_DIGEST_LENGTH];        
        return sha1;
    }
return nil;
}

Replace CC_SHA1 with CC_SHA256 (or whichever you need), as well as CC_SHA1_DIGEST_LENGTH with CC_SHA256_DIGEST_LENGTH.