Secure Hashes

If your application requires generation of secure hashes, you can use the raw Crypto APIs. These are actually C calls and do not have nice Objective C objects to interface with. The code snippet below shows how this is done for SHA-1. The input is any NSString and the output is a hex-encoded NSString version of the hashcode. If you need other types of hashing besides SHA-1, then you will need to change the SHA1 names in the functions and constants.

+ (NSString*) getHash:(NSString *) text
{
    NSData* myData =
         [text dataUsingEncoding:NSStringEncodingConversionAllowLossy];
    CC_SHA1_CTX ctx;
    uint8_t * hashBytes = NULL;
    NSData * hash = nil;

    // Malloc a buffer to hold hash.
    hashBytes = malloc( CC_SHA1_DIGEST_LENGTH * sizeof(uint8_t) );
    memset((void *)hashBytes, 0x0, CC_SHA1_DIGEST_LENGTH);

    // Initialize the context.
    CC_SHA1_Init(&ctx);
    // Perform the hash.
    CC_SHA1_Update(&ctx, (void *)[myData bytes], [myData length]);
    // Finalize the output.
    CC_SHA1_Final(hashBytes, &ctx);

    // Build up the SHA1 data.
    hash = [NSData dataWithBytes:(const void *)hashBytes
                          length:(NSUInteger)CC_SHA1_DIGEST_LENGTH];

    // if could not create, then exit otherwise clean up
    if(hashBytes)
      free(hashBytes);
    else
      return nil;

    // now return this as an hex-encoded string
    NSMutableString *stringBuffer = [NSMutableString
                                     stringWithCapacity:([hash length] * 2)];
    const unsigned char *dataBuffer = [hash bytes];
    int i;
    for (i = 0; i < [hash length]; ++i)
    {
        [stringBuffer appendFormat:@"%02X", (unsigned long)dataBuffer[i]];
    }

    return [[stringBuffer copy] autorelease];
}

One thing to note is the you need to include the following line:

#import <CommonCrypto/CommonDigest.h>

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