iPhone SHA-1 encoding different results from Rails?

Question

Ruby code:

  a = OpenSSL::HMAC.digest('sha1', 'secret', 'example')

and then:

 Base64.encode64(a).chomp

yields

 aMp6Zw1+hHVMmwWXoFp/Aaipc20=

iPhone:

+ (NSData *)hmac:(NSString *)input withKey:(NSString *)key {
    const char *cstrInput = [input cStringUsingEncoding:NSASCIIStringEncoding];
    const char *cstrKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
    NSData *data = [NSData dataWithBytes:cstrInput length:input.length];

    unsigned char chmac[CC_SHA1_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA1, cstrKey, strlen(cstrKey), data, [data length], &chmac);

    NSData *hmacData = [[NSData alloc] initWithBytes:chmac length:sizeof(chmac)];
    return [hmacData autorelease];
}

And

[XICrypto hmac:@"example" withKey:@"secret"];
NSLog(@"HMACData: %@",[HMACData description]);
NSString *HMACEncodedString = [HMACData base64Encoding];

(Where base64Encoding method is from Alex Reynold's answer on Cocoa Base 64 Implementation for REST Auth)

Results yield

Qm+ManmzmtfhpOzFdf8UHW43L5o=

So these methods are not performing the same operations, why?

EDIT: digest and key were backwards in the Rails call. Fixed that, yet the result is still different from the iPhone's call.

Have you looked here? I'm not sure you're using the correct function to perform your SHA-1 encryption - http://stackoverflow.com/questions/3468268/objective-c-sha1. — Perception, Jul 18 '11 at 15:52
CCHmac is supposed to be the 1 function call for init update and final. I am looking into the issue and string encoding is making the biggest difference. — Joe, Jul 18 '11 at 15:54
@Perception, I don't see the option for a secret key in that post. @Joe, Do you see any issue with the encoding? — quantumpotato, Jul 18 '11 at 16:15
Had the rails call key & data backwards as per the docs: HMAC.digest(digest, key, data) → aString Updated post with correct param order & new result aMp6Zw1+hHVMmwWXoFp/Aaipc20= — quantumpotato, Jul 18 '11 at 16:20
@quanumpotato - your right, you need to be able to pass in the key so the other post doesn't help much, if any. @Joe might be onto something with the character encoding. — Perception, Jul 18 '11 at 16:28

Joe · Accepted Answer · 2011-07-18T16:33:19.500

Yes I see your comment after I figured out that part on my own :), your rails call is backwards, your next issue is encoding. When ever you want the correct length of bytes when using string encoding use lengthOfBytesUsingEncoding:.

+ (NSData *)hmac:(NSString *)input withKey:(NSString *)key {
    NSStringEncoding encoding = NSASCIIStringEncoding;
    const char *cstrInput = [input cStringUsingEncoding:encoding];
    NSUInteger inputLength = [input lengthOfBytesUsingEncoding:encoding];
    const char *cstrKey = [key cStringUsingEncoding:encoding];
    NSUInteger keyLength = [key lengthOfBytesUsingEncoding:encoding];

    unsigned char chmac[CC_SHA1_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA1, cstrKey, keyLength, cstrInput, inputLength, &chmac);

    return [[[NSData alloc] initWithBytes:chmac length:sizeof(chmac)] autorelease];
}

I logged the contents of the data and get 68ca7a67 0d7e8475 4c9b0597 a05a7f01 a8a9736d and if you paste that into the hex field of this translator you will get aMp6Zw1+hHVMmwWXoFp/Aaipc20= in the base64 field.

Your orignal method could be fixed also by using strlen(cstrInput) when creating the data instead of input.length to make it a quick fix. — Joe, Jul 18 '11 at 16:57

iPhone SHA-1 encoding different results from Rails?

1 Answers1