Generate RSA Key and Sign a String

Demonstrates how to generate a new RSA public/private key pair and use it to generate a signature for a string. The (binary) digital signature is returned as a hexidecimalized string.

Download: Chilkat Cocoa Objective-C Libraries

NSMutableString *strOutput = [NSMutableString stringWithCapacity:1000];

CkoRsa *rsa = [[[CkoRsa alloc] init] autorelease];

//  Any string argument automatically begins the 30-day trial.
BOOL success;
success = [rsa UnlockComponent: @"30-day trial"];
if (success != YES) {
    [strOutput appendString: @"RSA component unlock failed"];
    [strOutput appendString: @"\n"];
    self.mainTextField.stringValue = strOutput;
    return;
}

//  Generate a 1024-bit RSA key pair.
[rsa GenerateKey: [NSNumber numberWithInt: 1024]];

//  This example will sign a string, and receive the signature
//  in a hex-encoded string.  Therefore, set the encoding mode
//  to "hex":
rsa.EncodingMode = @"hex";

//  If some other non-Chilkat application or web service is going to be verifying
//  the signature, it is important to match the byte-ordering.
//  The LittleEndian property may be set to YES
//  for little-endian byte ordering,
//  or NO  for big-endian byte ordering.
//  Microsoft apps typically use little-endian, while
//  OpenSSL and other services (such as Amazon CloudFront)
//  use big-endian.
rsa.LittleEndian = NO;

NSString *strData;
strData = @"This is the string to be signed.";

//  Sign the string using the  md5 hash algorithm.
//  Other valid choices are "md2", "sha256", "sha384",
//  "sha512", and "sha-1".
NSString *hexSig;
hexSig = [rsa SignStringENC: strData hashAlg: @"md5"];

[strOutput appendString: hexSig];
[strOutput appendString: @"\n"];
[strOutput appendString: rsa.LastErrorText];
[strOutput appendString: @"\n"];

//  Now verify the signature:
success = [rsa VerifyStringENC: strData hashAlg: @"md5" sig: hexSig];
if (success == YES) {
    [strOutput appendString: @"Signature verified!"];
    [strOutput appendString: @"\n"];
}
else {
    [strOutput appendString: rsa.LastErrorText];
    [strOutput appendString: @"\n"];
}

//  Try it with an invalid signature:
success = [rsa VerifyStringENC: strData hashAlg: @"md5" sig: @"not a valid sig"];
if (success == YES) {
    [strOutput appendString: @"Signature verified!"];
    [strOutput appendString: @"\n"];
}
else {
    [strOutput appendString: rsa.LastErrorText];
    [strOutput appendString: @"\n"];
}

//  Try it with invalid data:
success = [rsa VerifyStringENC: @"Not the original data" hashAlg: @"md5" sig: hexSig];
if (success == YES) {
    [strOutput appendString: @"Signature verified!"];
    [strOutput appendString: @"\n"];
}
else {
    [strOutput appendString: rsa.LastErrorText];
    [strOutput appendString: @"\n"];
}

//  Try it with the wrong hash algorithm:
success = [rsa VerifyStringENC: strData hashAlg: @"sha-1" sig: hexSig];
if (success == YES) {
    [strOutput appendString: @"Signature verified!"];
    [strOutput appendString: @"\n"];
}
else {
    [strOutput appendString: rsa.LastErrorText];
    [strOutput appendString: @"\n"];
}


self.mainTextField.stringValue = strOutput;