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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.
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For SHA-256 these are calculated from the first 8 primes. These always remain the same for any message. The primes are firstly square rooted and then taken to the modulus 1. The result is then multiplied by 16⁸ and rounded down to the nearest integer.
If you see “SHA-2,” “SHA-256” or “SHA-256 bit,” those names are referring to the same thing. If you see “SHA-224,” “SHA-384,” or “SHA-512,” those are referring to the alternate bit-lengths of SHA-2.
SHA-2 is often called the SHA-2 family of hashes because it contains many different-size hashes, including 224-, 256-, 384-, and 512-bit digests. When someone says they are using the SHA-2 hash, you don't know which bit length they are using, but the most popular one is 256 bits (by a large margin).
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.
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