DecryptData.swift

let algorithm: SecKeyAlgorithm = .eciesEncryptionStandardX963SHA1AESGCM

func decrypt(string: String) -> String? {
    let attributes: [String: Any] = [
            kSecClass as String: kSecClassKey,
            kSecAttrApplicationTag as String: "com.cardosoedgar.key",
            kSecReturnRef as String: true]

    var key: CFTypeRef?
    let status = SecItemCopyMatching(attributes as CFDictionary, &key)
    guard status == errSecSuccess else { return nil }

    var error: Unmanaged<CFError>?
    guard let data = Data(base64Encoded: string), 
          let decrypted = SecKeyCreateDecryptedData(key as! SecKey, algorithm, data as CFData, &error) else { return nil }
    return String(data: decrypted as Data, encoding: .utf8)
}