Created
July 26, 2019 16:04
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HKDF implementation in Swift using Apple's CryptoKit framework
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| func hkdf_sha256(_ seed: Data, salt: Data, info: Data, outputSize: Int = 32) -> Data? { | |
| // It would be nice to make this generic over <H: HashFunction> if HashFunction had byteCount instead of each hash | |
| // individually implementing it. | |
| let iterations = UInt8(ceil(Double(outputSize) / Double(SHA256.byteCount))) | |
| guard iterations <= 255 else { | |
| return nil | |
| } | |
| let prk = HMAC<SHA256>.authenticationCode(for: seed, using: SymmetricKey(data: salt)) | |
| let key = SymmetricKey(data: prk) | |
| var hkdf = Data() | |
| var value = Data() | |
| for i in 1...iterations { | |
| value.append(info) | |
| value.append(i) | |
| let code = HMAC<SHA256>.authenticationCode(for: value, using: key) | |
| hkdf.append(contentsOf: code) | |
| value = Data(code) | |
| } | |
| return hkdf.prefix(outputSize) | |
| } |
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