Saving RSA public key in iOS keychain using kSecAttrAccessible

Question

So, I know that I can store the RSA key in the keychain using the following code:

+ (void)savePublicKeyToKeychain:(NSData *)key tag:(NSString *)tagString deleteExisting:(BOOL)deleteExisting {
    NSData *tag = [SecKeyWrapper getKeyTag:tagString];

    NSDictionary *saveDict = @{
            (__bridge id) kSecClass : (__bridge id) kSecClassKey,
            (__bridge id) kSecAttrKeyType : (__bridge id) kSecAttrKeyTypeRSA,
            (__bridge id) kSecAttrApplicationTag : tag,
            (__bridge id) kSecAttrKeyClass : (__bridge id) kSecAttrKeyClassPublic,
            (__bridge id) kSecValueData : key
    };
    [self saveKeyToKeychain:saveDict tag:tagString deleteExisting:deleteExisting];
}

+ (void)saveKeyToKeychain:(NSDictionary *)saveDict tag:(NSString *)tagString deleteExisting:(BOOL)deleteExisting {
    OSStatus sanityCheck = SecItemAdd((__bridge CFDictionaryRef) saveDict, NULL);
    if (sanityCheck != errSecSuccess) {
        if (sanityCheck == errSecDuplicateItem && deleteExisting) {
            // delete the duplicate and save again
            SecItemDelete((__bridge CFDictionaryRef) saveDict);
            sanityCheck = SecItemAdd((__bridge CFDictionaryRef) saveDict, NULL);
        }
        if (sanityCheck != errSecSuccess) {
            NSLog(@"Problem saving the key to keychain, OSStatus == %d.", (int) sanityCheck);
        }
    }
    // remove from cache
    [keyCache removeObjectForKey:tagString];
}

This I can save and receive correctly. If I try to set the value kSecAttrAccessibleto save:

+ (void)savePublicKeyToKeychain:(NSData *)key tag:(NSString *)tagString deleteExisting:(BOOL)deleteExisting {
    NSData *tag = [SecKeyWrapper getKeyTag:tagString];

    NSDictionary *saveDict = @{
            (__bridge id) kSecClass : (__bridge id) kSecClassKey,
            (__bridge id) kSecAttrKeyType : (__bridge id) kSecAttrKeyTypeRSA,
            (__bridge id) kSecAttrApplicationTag : tag,
            (__bridge id) kSecAttrKeyClass : (__bridge id) kSecAttrKeyClassPublic,
            (__bridge id) kSecAttrAccessible: (__bridge id) kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly,
            (__bridge id) kSecValueData : key
    };
    [self saveKeyToKeychain:saveDict tag:tagString deleteExisting:deleteExisting];
}

and then, trying to get it, I get junk. This is garbage, because when I retrieve it immediately after saving, the inserted value and the received value are different.

Does anyone have a sample code or know how to set the accessibility of a keychain element, especially for an RSA key?

Answer 1

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