I liked the way Grokking the coding interview organized problems into learnable patterns. However, the course is expensive and the majority of the time the problems are copy-pasted from leetcode. As the explanations on leetcode are usually just as good, the course really boils down to being a glorified curated list of leetcode problems.
So below I made a list of leetcode problems that are as close to grokking problems as possible.
| func verifySignature(text2sign : String, signature : Data) throws -> Void | |
| { | |
| var error: Unmanaged<CFError>? | |
| let privateKey = try! retrievePrivateKey() | |
| let publicKey = SecKeyCopyPublicKey(privateKey) | |
| let algorithm: SecKeyAlgorithm = .ecdsaSignatureMessageX962SHA512 | |
| // Check if selected algorithm suits the key’s capabilities. | |
| guard SecKeyIsAlgorithmSupported(publicKey!, .verify, algorithm) else { | |
| throw error!.takeRetainedValue() as Error |
| func sign(text2sign : String) throws -> Data { | |
| var error: Unmanaged<CFError>? | |
| let privateKey = try! retrievePrivateKey() | |
| let algorithm: SecKeyAlgorithm = .ecdsaSignatureMessageX962SHA512 | |
| guard SecKeyIsAlgorithmSupported(privateKey, .sign, algorithm) else { | |
| throw error!.takeRetainedValue() as Error | |
| } | |
| let data2sign = text2sign.data(using: .utf8)! |
| func encrypt(text: String) throws -> Void { | |
| let privateKey = try! retrievePrivateKey() | |
| let publicKey = SecKeyCopyPublicKey(privateKey) | |
| let algorithm: SecKeyAlgorithm = .eciesEncryptionCofactorX963SHA256AESGCM | |
| // Check if selected algorithm suits the key’s capabilities. | |
| var error: Unmanaged<CFError>? | |
| guard SecKeyIsAlgorithmSupported(publicKey!, .encrypt, algorithm) else { | |
| throw error!.takeRetainedValue() as Error |
| func retrievePrivateKey() throws -> SecKey { | |
| // Create a query with key type and tag | |
| let getQuery: [String: Any] = [kSecClass as String: kSecClassKey, | |
| kSecAttrApplicationTag as String: TAG, | |
| kSecAttrKeyType as String: kSecAttrKeyTypeECSECPrimeRandom, | |
| kSecReturnRef as String: true] | |
| // Use this query with the SecItemCopyMatching method to execute a search | |
| var item: CFTypeRef? | |
| let status = SecItemCopyMatching(getQuery as CFDictionary, &item) |
| func createECCKeyPair () throws -> Void { | |
| let attributes: [String: Any] = | |
| [kSecAttrKeyType as String: kSecAttrKeyTypeECSECPrimeRandom, // only supported key type for ECC | |
| kSecAttrKeySizeInBits as String: 521, // supported key lengths: 256, 383 and 521 | |
| kSecPrivateKeyAttrs as String: | |
| [kSecAttrIsPermanent as String: true, | |
| kSecAttrApplicationTag as String: TAG] | |
| ] | |
| // The key is generated and stored in the default keychain |
| public void verify(String message, byte[] signedData) throws Exception { | |
| KeyPair keyPair = getKeys(); | |
| Signature signature = Signature.getInstance("SHA256withECDSA"); | |
| signature.initVerify(keyPair.getPublic()); | |
| signature.update(message.getBytes()); | |
| boolean verified = signature.verify(signedData); | |
| if (verified) Log.d("_MK", "Signature verified"); | |
| else Log.d("_MK", "Verification failed"); | |
| } |
| /** | |
| * Supported signature algorithms: | |
| * https://developer.android.com/reference/java/security/Signature | |
| */ | |
| public byte[] sign(String message) throws Exception { | |
| KeyPair keyPair = getKeys(); | |
| Signature signature = Signature.getInstance("SHA256widthECDSA"); | |
| signature.initSign(keyPair.getPrivate()); | |
| signature.update(message.getBytes()); |
| public void generateKeyPair() throws NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException { | |
| KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance( | |
| KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore"); | |
| keyPairGenerator.initialize(new KeyGenParameterSpec.Builder( | |
| TAG, | |
| KeyProperties.PURPOSE_SIGN) | |
| // Supported curves: [p-224, p-256, p-384, p-521, prime256v1, secp224r1, secp256r1, secp384r1, secp521r1] | |
| .setAlgorithmParameterSpec(new ECGenParameterSpec("secp521r1")) | |
| .setDigests(KeyProperties.DIGEST_SHA256, |
| public void generateRsaKeyPairForEncrypiton(final String TAG) throws Exception { | |
| KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore"); | |
| keyPairGenerator.initialize(new KeyGenParameterSpec.Builder( | |
| TAG, | |
| KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT) | |
| .setBlockModes(KeyProperties.BLOCK_MODE_ECB) | |
| .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1) | |
| .build()); |