问在iOS/Swift中创建并导出为base64的RSA公钥

EN

class RSAKeyEncoding: NSObject {

  // ASN.1 identifiers
  private let bitStringIdentifier: UInt8 = 0x03
  private let sequenceIdentifier: UInt8 = 0x30

  // ASN.1 AlgorithmIdentfier for RSA encryption: OID 1 2 840 113549 1 1 1 and NULL
  private let algorithmIdentifierForRSAEncryption: [UInt8] = [0x30, 0x0d, 0x06,
    0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00]

  /// Converts the DER encoding of an RSA public key that is either fetched from the
  /// keychain (e.g. by using `SecItemCopyMatching(_:_:)`) or retrieved in another way
  /// (e.g. by using `SecKeyCopyExternalRepresentation(_:_:)`), to a format typically
  /// used by tools and programming languages outside the Apple ecosystem (such as
  /// OpenSSL, Java, PHP and Perl). The DER encoding of an RSA public key created by
  /// iOS is represented with the ASN.1 RSAPublicKey type as defined by PKCS #1.
  /// However, many systems outside the Apple ecosystem expect the DER encoding of a
  /// key to be represented with the ASN.1 SubjectPublicKeyInfo type as defined by
  /// X.509. The two types are related in a way that if the SubjectPublicKeyInfo’s
  /// algorithm field contains the rsaEncryption object identifier as defined by
  /// PKCS #1, the subjectPublicKey field shall contain the DER encoding of an
  /// RSAPublicKey type.
  ///
  /// - Parameter rsaPublicKeyData: A data object containing the DER encoding of an
  ///     RSA public key, which is represented with the ASN.1 RSAPublicKey type.
  /// - Returns: A data object containing the DER encoding of an RSA public key, which
  ///     is represented with the ASN.1 SubjectPublicKeyInfo type.
  func convertToX509EncodedKey(_ rsaPublicKeyData: Data) -> Data {
    var derEncodedKeyBytes = [UInt8](rsaPublicKeyData)

    // Insert ASN.1 BIT STRING bytes at the beginning of the array
    derEncodedKeyBytes.insert(0x00, at: 0)
    derEncodedKeyBytes.insert(contentsOf: lengthField(of: derEncodedKeyBytes), at: 0)
    derEncodedKeyBytes.insert(bitStringIdentifier, at: 0)

    // Insert ASN.1 AlgorithmIdentifier bytes at the beginning of the array
    derEncodedKeyBytes.insert(contentsOf: algorithmIdentifierForRSAEncryption, at: 0)

    // Insert ASN.1 SEQUENCE bytes at the beginning of the array
    derEncodedKeyBytes.insert(contentsOf: lengthField(of: derEncodedKeyBytes), at: 0)
    derEncodedKeyBytes.insert(sequenceIdentifier, at: 0)

    return Data(derEncodedKeyBytes)
  }

  private func lengthField(of valueField: [UInt8]) -> [UInt8] {
    var length = valueField.count

    if length < 128 {
      return [ UInt8(length) ]
    }

    // Number of bytes needed to encode the length
    let lengthBytesCount = Int((log2(Double(length)) / 8) + 1)

    // First byte encodes the number of remaining bytes in this field
    let firstLengthFieldByte = UInt8(128 + lengthBytesCount)

    var lengthField: [UInt8] = []
    for _ in 0..<lengthBytesCount {
      // Take the last 8 bits of length
      let lengthByte = UInt8(length & 0xff)
      // Insert them at the beginning of the array
      lengthField.insert(lengthByte, at: 0)
      // Delete the last 8 bits of length
      length = length >> 8
    }

    // Insert firstLengthFieldByte at the beginning of the array
    lengthField.insert(firstLengthFieldByte, at: 0)

    return lengthField
  }
}

extension SecKey {
  func asBase64() throws -> String {
    var dataPtr: CFTypeRef?
    let query: [String:Any] = [
      kSecClass as String: kSecClassKey,
      kSecAttrApplicationTag as String: "...", // Same unique tag here
      kSecAttrKeyType as String: kSecAttrKeyTypeRSA,
      kSecReturnData as String: kCFBooleanTrue
    ]
    let result = SecItemCopyMatching(query as CFDictionary, &dataPtr)

    switch (result, dataPtr) {
    case (errSecSuccess, .some(let data)):

      // convert to X509 encoded key
      let convertedData = RSAKeyEncoding().convertToX509EncodedKey(data)

      // convert to Base64 string
      let base64PublicKey = convertedData.base64EncodedString(options: [])
      return base64PublicKey
    default:
      throw CryptoError.keyConversionError
    }
  }
}

let keySize = ... // Key size specified when storing the key, for example: 2048

let query: [String: Any] = [
    kSecAttrKeySizeInBits as String: keySize,
    kSecAttrEffectiveKeySize as String: keySize,
    ... // More attributes
]

var dataPtr: CFTypeRef?

let result = SecItemCopyMatching(query as CFDictionary, &dataPtr)

func exportPublicKeyToDER(keyId:String) -> NSData?{

    let publicKey = loadKeyStringFromKeyChainAsNSData(PUBLIC_KEY + keyId)
    let keyType = kSecAttrKeyTypeRSA
    let keySize = 2048
    let exportImportManager = CryptoExportImportManager()
    if let exportableDERKey = exportImportManager.exportPublicKeyToDER(publicKey, keyType: keyType as String, keySize: keySize) {
        return exportableDERKey
    } else {
        return nil
    }
}