Invalid signature: oauth_signature

Question

I am trying to produce oauth_signature to use Fatsecret API, but getting invalid signature error - can't figure out why. I tried to follow all steps mentioned here (see step 2) for Signature value generation as accurately as possible. They say:

Use the HMAC-SHA1 signature algorithm as defined by the [RFC2104] to sign the request where text is the Signature Base String and key is the concatenated values of the Consumer Secret and Access Secret separated by an '&' character (show '&' even if Access Secret is empty as some methods do not require an Access Token).

The calculated digest octet string, first base64-encoded per [RFC2045], then escaped using the [RFC3986] percent-encoding (%xx) mechanism is the oauth_signature.

For base64 encoding, I used QSStrings.h

Steps I coded are as follows:

- (void)viewDidLoad
{
NSTimeInterval intervalFloat = [[NSDate date] timeIntervalSince1970];
int interval = (int) intervalFloat;
NSLog(@"time interval: %d",interval);

//for oauth_nonce random string
NSString *randomString = [self genRandString]; //see definition below
NSLog(@"%@",randomString);

NSString *requestString = [NSString stringWithFormat:@"POST&http%3A%2F%2Fplatform.fatsecret.com%2Frest%2Fserver.api&format%3Djson%26method%3Dprofile.create%26oauth_consumer_key%3Db753c99ccxxxxxx%26oauth_nonce%3D%@%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D%d%26oauth_version%3D1.0",randomString,interval];
NSString *secret = @"3959096c04xxxxxxxx&";

NSString *encodedStr = [self hmacsha1:requestString secret:secret]; //see definition below
NSLog(@"encodedStr: %@",encodedStr);

NSString *encodedString = [self urlEncodeValue:encodedStr]; //see definition below
NSLog(@"encodedString: %@",encodedString);

NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://platform.fatsecret.com/rest/server.api?format=json&method=profile.create&oauth_consumer_key=b753c99ccxxxxxx&oauth_nonce=%@&oauth_signature=%@&oauth_signature_method=HMAC-SHA1&oauth_timestamp=%d&oauth_version=1.0",randomString, encodedString,interval]];
           
_request = [ASIFormDataRequest requestWithURL:url];
[_request setPostValue:@"json" forKey:@"format"];
[_request setPostValue:@"profile.create" forKey:@"method"];
[_request setPostValue:@"b753c99ccxxxxxx" forKey:@"oauth_consumer_key"];
[_request setPostValue:randomString forKey:@"oauth_nonce"];
[_request setPostValue:encodedString forKey:@"oauth_signature"];
[_request setPostValue:@"HMAC-SHA1" forKey:@"oauth_signature_method"];
[_request setPostValue:[NSNumber numberWithInt:interval] forKey:@"oauth_timestamp"];
[_request setPostValue:@"1.0" forKey:@"oauth_version"];

[_request setDelegate:self];
_request.timeOutSeconds = 60.0; 
[_request startAsynchronous];

}

Definitions for methods I used in code above are as follows:

- (NSString *)hmacsha1:(NSString *)data secret:(NSString *)key {

const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];

unsigned char cHMAC[CC_SHA1_DIGEST_LENGTH];

CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];

NSString *hash = [QSStrings encodeBase64WithData:HMAC];

NSLog(@"Hash: %@", hash);  

return hash;
}

NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

-(NSString *) genRandString {
//fixing length of 4 chars
NSMutableString *randomString = [NSMutableString stringWithCapacity: 4];

for (int i=0; i<4; i++) {
    [randomString appendFormat: @"%C", [letters characterAtIndex: arc4random() % [letters length]]];
}

return randomString;
}

- (NSString *)urlEncodeValue:(NSString *)str
{
NSMutableString * output = [NSMutableString string];
const unsigned char * source = (const unsigned char *)[str UTF8String];
int sourceLen = strlen((const char *)source);
for (int i = 0; i < sourceLen; ++i) {
    const unsigned char thisChar = source[i];
    if (thisChar == ' '){
        [output appendString:@"+"];
    } else if (thisChar == '.' || thisChar == '-' || thisChar == '_' || thisChar == '~' || 
               (thisChar >= 'a' && thisChar <= 'z') ||
               (thisChar >= 'A' && thisChar <= 'Z') ||
               (thisChar >= '0' && thisChar <= '9')) {
        [output appendFormat:@"%c", thisChar];
    } else {
        [output appendFormat:@"%%%02X", thisChar];
    }
}
return output;
}

You can see problem by downloading my project from here

Answer 1

Atlast I myself figured out the mistakes in the code. Nearly 80% problem has been solved. I was doing wrong at this place:

NSString *requestString = [NSString stringWithFormat:@"POST&http%3A%2F%2Fplatform.fatsecret.com%2Frest%2Fserver.api&format%3Djson%26method%3Dprofile.create%26oauth_consumer_key%3Db753c99ccxxxxxx%26oauth_nonce%3D%@%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D%d%26oauth_version%3D1.0",randomString,interval];

Here I pre-encoded the base string. As I am initializing string with some format, it was taking http%3A%2F%2F as some sort of unknown format, replacing it with 0's. So I replaced whole code as:

- (void)viewDidLoad
{
[super viewDidLoad];

//for timestamp
NSTimeInterval intervalFloat = [[NSDate date] timeIntervalSince1970];
int interval = (int) intervalFloat;
NSLog(@"time interval: %d",interval);

//for oauth_nonce random string
NSString *randomString = [self genRandString];
NSLog(@"%@",randomString);

NSString *actualString = [NSString stringWithFormat:@"format=json&method=profile.create&oauth_consumer_key=b753c99ccd8****&oauth_nonce=%@&oauth_signature_method=HMAC-SHA1&oauth_timestamp=%d&oauth_version=1.0",randomString,interval];

 NSString *firstEncode = [self urlEncodeValue:actualString];

NSLog(@"first encode: %@",firstEncode);

NSMutableString *requestString = [[NSMutableString alloc] initWithString:@"GET&http%3A%2F%2Fplatform.fatsecret.com%2Frest%2Fserver.api&"];
[requestString appendString:firstEncode];
NSLog(@"base str: %@",requestString);

NSString *secret = @"395********&";

NSString *encodedStr = [self hmacsha1:requestString secret:secret];
NSLog(@"encodedStr: %@",encodedStr);

NSString *encodedString = [self urlEncodeValue:encodedStr];
NSLog(@"encodedString: %@",encodedString);

NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"http://platform.fatsecret.com/rest/server.api?format=json&method=profile.create&oauth_consumer_key=b753c99cc*******&oauth_nonce=%@&oauth_signature=%@&oauth_signature_method=HMAC-SHA1&oauth_timestamp=%d&oauth_version=1.0",randomString, encodedString,interval]];
NSLog(@"url: %@",url);

_request = [ASIFormDataRequest requestWithURL:url];
[_request setPostValue:@"json" forKey:@"format"];
[_request setPostValue:@"profile.create" forKey:@"method"];
[_request setPostValue:@"b753c9*********" forKey:@"oauth_consumer_key"];
[_request setPostValue:randomString forKey:@"oauth_nonce"];
[_request setPostValue:encodedString forKey:@"oauth_signature"];
[_request setPostValue:@"HMAC-SHA1" forKey:@"oauth_signature_method"];
[_request setPostValue:[NSNumber numberWithInt:interval] forKey:@"oauth_timestamp"];
[_request setPostValue:@"1.0" forKey:@"oauth_version"];

[_request setRequestMethod:@"GET"];
[_request addRequestHeader:@"Content-Type" value:@"application/json"];
[_request setDelegate:self];
_request.timeOutSeconds = 60.0; 
[_request startAsynchronous];

}

I hope this helps someone.