Need to generate HMAC SHA256 hash in Objective C as in Java
Solution 1
You need to fix your Java hmac printer, because 4effffffd8ffffffce7cffffffc4ffffffc71b2f72ffffffdc21ffffffa1ffffffe0ffffffe62d32550b0771296bffffff9c1159ffffffdeffffff8675ffffff9928654c
isn't valid. All those ffffff
in there are a giveaway that you are sign-extending the bytes to 32-bit signed integers before converting them to hex. Presumably the correct hmac is 4ed8ce7cc4c71b2f72dc21a1e0e62d32550b0771296b9c1159de86759928654c
.
Anyway, I suspect you are calling your method incorrectly. I copied your code into a test program which gives me this output for your key and data:
2011-12-10 13:03:38.231 hmactest[8251:707] test hmac = <4ed8ce7c c4c71b2f 72dc21a1 e0e62d32 550b0771 296b9c11 59de8675 9928654c>
That matches your desired output (except for the sign-extension errors).
Here's my test program:
#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonHMAC.h>
NSData *hmacForKeyAndData(NSString *key, NSString *data)
{
const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];
unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
return [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];
}
int main (int argc, const char * argv[])
{
@autoreleasepool {
// Compare to http://en.wikipedia.org/wiki/HMAC#Examples_of_HMAC_.28MD5.2C_SHA1.2C_SHA256_.29
NSLog(@"empty hmac = %@", hmacForKeyAndData(@"", @""));
NSLog(@"test hmac = %@", hmacForKeyAndData(@"YARJSuwP5Oo6/r47LczzWjUx/T8ioAJpUK2YfdI/ZshlTUP8q4ujEVjC0seEUAAtS6YEE1Veghz+IDbNQb+2KQ==", @"id=456|time=19:10|nonce=8"));
}
return 0;
}
Solution 2
Line
CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
has a bug
If in your key would be 0x00 byte strlen(cKey)
would give wrong length and hmac generation process will produce some rubbish.
In my implementation I have changed that to:
CCHmac(kCCHmacAlgSHA256, cKey, [key length], cData, [data length], cHMAC);
Tushar
A Geek, Entrepreneur ! Building a lot of SaaS applications for SMEs. The recent ones are: https://www.HRStop.com https://www.HiringBull.com https://www.HawkHR.com Recently published two open source projects - Database documenter - http://dbdoc.codeplex.com Database Script Executer - http://sqlexecuter.codeplex.com
Updated on June 14, 2022Comments
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Tushar about 2 years
I need to generate a hash using HMAC SHA256. I am using the following code in Java. I need an equivalent code in Objective-C.
javax.crypto.Mac mac = javax.crypto.Mac.getInstance(type); javax.crypto.spec.SecretKeySpec secret = new javax.crypto.spec.SecretKeySpec(key.getBytes(), type); mac.init(secret); byte[] digest = mac.doFinal(value.getBytes()); StringBuilder sb = new StringBuilder(digest.length * 2); String s=""; for (byte b: digest) { s = Integer.toHexString(b); if (s.length() == 1) { sb.append('0'); } sb.append(s); } return sb.toString();
Key =
YARJSuwP5Oo6/r47LczzWjUx/T8ioAJpUK2YfdI/ZshlTUP8q4ujEVjC0seEUAAtS6YEE1Veghz+IDbNQb+2KQ==
Value =
id=456|time=19:10|nonce=8
Output =
4effffffd8ffffffce7cffffffc4ffffffc71b2f72ffffffdc21ffffffa1ffffffe0ffffffe62d32550b0771296bffffff9c1159ffffffdeffffff8675ffffff9928654c
I have this Objective-C function:
//Hash method Definition - (NSString *)getHashEncription:(NSString *)key andData:(NSString *)data{ NSLog(@"Secret Key %@ And Data %@", key, data); const char *cKey = [key cStringUsingEncoding:NSASCIIStringEncoding]; const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding]; unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH]; //HmacSHA256 CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC); NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)]; [Base64 initialize]; NSString *b64EncStr = [Base64 encode:HMAC]; NSLog(@"Base 64 encoded = %@",b64EncStr); NSLog(@"NSData Value %@", HMAC); // unsigned char hashedChars[32]; // NSString *inputString; // inputString = [NSString stringWithFormat:@"hello"]; // NSData * inputData = [inputString dataUsingEncoding:NSUTF8StringEncoding]; // CC_SHA256(inputData.bytes, inputData.length, hashedChars); return [[NSString alloc] initWithData:HMAC encoding:NSASCIIStringEncoding]; }//End of getHashEncription
The output that I am getting is this:
8736bc4aa7fc3aa071f2b4262b6972a89d2861559a20afa765e46ff17cb181a9
I tried removing the base64 encoding, but it didn't work.
Any suggestions are most welcome.
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gdubs over 11 yearshi, so im having the same problem and your solution helped me solve the inaccuracy of the hmac i generate from ios. my only problem is tho when it returns NSData it the return looks like this <2efb00ab a01a3f5b 674fba30.....> it would basically have spaces. Meanwhile on my API it would be one whole string ("2efb00aba01a3f5b674fba3063b43fee7a93569471...."). I'm using c# btw for the api. my question is do I just remove the spaces so I can pass the correct signature to my api? or do i convert it to string using base64 (this will change the value tho)?
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Muhammad Saad Ansari over 10 yearsCCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC); <-- on this line i am getting EXC_BAD_ACESS . Any idea ?
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CommaToast over 8 yearsDon't you need to free(cHMAC)? To avoid unbounded memory growth from this? And why isn't it a pointer..?
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rob mayoff over 8 yearsYou don't need to free it, because it is allocated on the stack.
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Olie about 8 yearsThe problem I'm having is that my particular data (I'm using the same hMac routines you guys are), when I do
const char *cData = [data cStringUsingEncoding: NSASCIIStringEncoding];
, returns cData = NULL. Now I just have to figure out why. (I have a very narrow "this data worked, now this slightly modified data doesn't" test case, I just need to diff them and figure it out.) -
rob mayoff about 8 yearsThere are characters in your
data
string that do not exist in the ASCII character set.