(Objective-C) Compute JWK Thumbprint for RSA and EC Public Keys

Demonstrates how to compute a JSON Web Key thumbprint for a public key (RSA or ECC).

Note: This example requires Chilkat v9.5.0.66 or greater.

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#import <CkoPublicKey.h>
#import <CkoStringBuilder.h>

CkoPublicKey *pubKey = [[CkoPublicKey alloc] init];

// A public key can be loaded from any format (binary DER, PEM, etc.)
// This example will load the public keys from JWK format, 
// and will then compute the JWK thumbprint.

// First do it for an RSA public key...

CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
[sb Append: @"{"];
[sb Append: @"\"kty\": \"RSA\","];
[sb Append: @"\"n\": \"0vx7agoebGcQSuuPiLJXZptN9nndrQmbXEps2aiAFbWhM78LhWx4cbbfAAt"];
[sb Append: @"VT86zwu1RK7aPFFxuhDR1L6tSoc_BJECPebWKRXjBZCiFV4n3oknjhMstn6"];
[sb Append: @"4tZ_2W-5JsGY4Hc5n9yBXArwl93lqt7_RN5w6Cf0h4QyQ5v-65YGjQR0_FD"];
[sb Append: @"W2QvzqY368QQMicAtaSqzs8KJZgnYb9c7d0zgdAZHzu6qMQvRL5hajrn1n9"];
[sb Append: @"1CbOpbISD08qNLyrdkt-bFTWhAI4vMQFh6WeZu0fM4lFd2NcRwr3XPksINH"];
[sb Append: @"aQ-G_xBniIqbw0Ls1jF44-csFCur-kEgU8awapJzKnqDKgw\","];
[sb Append: @"\"e\": \"AQAB\","];
[sb Append: @"\"alg\": \"RS256\","];
[sb Append: @"\"kid\": \"2011-04-29\""];
[sb Append: @"}"];

// The JWK format is automatically detected..
BOOL success = [pubKey LoadFromString: [sb GetAsString]];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

// Get the JWK thumbprint (using SHA256)
NSLog(@"%@%@",@"JWK thumbprint: ",[pubKey GetJwkThumbprint: @"SHA256"]);

// Output:
// JWK thumbprint: NzbLsXh8uDCcd-6MNwXF4W_7noWXFZAfHkxZsRGC9Xs

// --------------------------------------------------------------
// Now let's do an EC public key:
[sb Clear];
[sb Append: @"{ "];
[sb Append: @"  \"kty\": \"EC\","];
[sb Append: @"  \"crv\": \"P-256\","];
[sb Append: @"  \"x\": \"tDeeYABgKEAbWicYPCEEI8sP4SRIhHKcHDW7VqrB4LA\","];
[sb Append: @"  \"y\": \"J08HOoIZ0rX2Me3bNFZUltfxIk1Hrc8FsLu8VaSxsMI\""];
[sb Append: @"}"];

success = [pubKey LoadFromString: [sb GetAsString]];
if (success != YES) {
    NSLog(@"%@",pubKey.LastErrorText);
    return;
}

// Get the JWK thumbprint (using SHA256)
NSLog(@"%@%@",@"JWK thumbprint: ",[pubKey GetJwkThumbprint: @"SHA256"]);

// Output:
// JWK thumbprint: 8fm8079s3nu4FLV_7dVJoJ69A8XCXn7Za2mtaWCnxR4