Converting Raw RSA Key value to SecKeyRef Object for Encryption

Question

Hi I have a RSa publicKey value in base64 , how do i convert to SecKeyRef Object without adding to Keychain Can i add a RSA Raw value to Keychain which is not in X509 format ???

thanks in advance

Answer 1

The following code comes from Apple's CryptoExercise example, in SecKeyWrapper.m. It assumes the "publicKey" NSData object is the binary DER-encoded ASN.1 object, not base-64 encoded. So you'll have to get a base-64 decoder and apply it first. You might also want to read this post in the Apple Developer Forums.

- (SecKeyRef)addPeerPublicKey:(NSString *)peerName keyBits:(NSData *)publicKey {
    OSStatus sanityCheck = noErr;
    SecKeyRef peerKeyRef = NULL;
    CFTypeRef persistPeer = NULL;

    LOGGING_FACILITY( peerName != nil, @"Peer name parameter is nil." );
    LOGGING_FACILITY( publicKey != nil, @"Public key parameter is nil." );

    NSData * peerTag = [[NSData alloc] initWithBytes:(const void *)[peerName UTF8String] length:[peerName length]];
    NSMutableDictionary * peerPublicKeyAttr = [[NSMutableDictionary alloc] init];

    [peerPublicKeyAttr setObject:(id)kSecClassKey forKey:(id)kSecClass];
    [peerPublicKeyAttr setObject:(id)kSecAttrKeyTypeRSA forKey:(id)kSecAttrKeyType];
    [peerPublicKeyAttr setObject:peerTag forKey:(id)kSecAttrApplicationTag];
    [peerPublicKeyAttr setObject:publicKey forKey:(id)kSecValueData];
    [peerPublicKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(id)kSecReturnPersistentRef];

    sanityCheck = SecItemAdd((CFDictionaryRef) peerPublicKeyAttr, (CFTypeRef *)&persistPeer);

    // The nice thing about persistent references is that you can write their value out to disk and
    // then use them later. I don't do that here but it certainly can make sense for other situations
    // where you don't want to have to keep building up dictionaries of attributes to get a reference.
    // 
    // Also take a look at SecKeyWrapper's methods (CFTypeRef)getPersistentKeyRefWithKeyRef:(SecKeyRef)key
    // & (SecKeyRef)getKeyRefWithPersistentKeyRef:(CFTypeRef)persistentRef.

    LOGGING_FACILITY1( sanityCheck == noErr || sanityCheck == errSecDuplicateItem, @"Problem adding the peer public key to the keychain, OSStatus == %d.", sanityCheck );

    if (persistPeer) {
        peerKeyRef = [self getKeyRefWithPersistentKeyRef:persistPeer];
    } else {
        [peerPublicKeyAttr removeObjectForKey:(id)kSecValueData];
        [peerPublicKeyAttr setObject:[NSNumber numberWithBool:YES] forKey:(id)kSecReturnRef];
        // Let's retry a different way.
        sanityCheck = SecItemCopyMatching((CFDictionaryRef) peerPublicKeyAttr, (CFTypeRef *)&peerKeyRef);
    }

    LOGGING_FACILITY1( sanityCheck == noErr && peerKeyRef != NULL, @"Problem acquiring reference to the public key, OSStatus == %d.", sanityCheck );

    [peerTag release];
    [peerPublicKeyAttr release];
    if (persistPeer) CFRelease(persistPeer);
    return peerKeyRef;
}