swift 在iOS10之后，支持ecdh加解密。

1.生成公钥和私钥。

   func generateKey() {
        
        let attributes: [String: Any] = [kSecAttrKeySizeInBits as String: 256,
                                         kSecAttrKeyType as String: kSecAttrKeyTypeEC,
                                         kSecPrivateKeyAttrs as String: [kSecAttrIsPermanent as String: false]]
        var error: Unmanaged<CFError>?
        
        self.privateKey = SecKeyCreateRandomKey(attributes as CFDictionary, &error)
        
        if self.privateKey != nil {
            self.publicKey = SecKeyCopyPublicKey(self.privateKey!)
        }
    }

2.加密

func encryptedData(sourceData: Data, algorithm:SecKeyAlgorithm) -> Data? {
        
        guard self.publicKey != nil else {
            return nil
        }
        
        var error: Unmanaged<CFError>?
        
        let encrypted =
            SecKeyCreateEncryptedData(self.publicKey!, algorithm,
                                      sourceData as CFData,
                                      &error)
        if error == nil {
            return encrypted! as Data
        }
        
        return nil
    }

3.解密

   func decryptedData(sourceData: Data, algorithm:SecKeyAlgorithm ) -> String? {
        
        var error: Unmanaged<CFError>?
        
        let resData = SecKeyCreateDecryptedData(self.privateKey! , algorithm,
                                                sourceData as CFData, &error)
        
        if error == nil {
            return String(data: resData! as Data, encoding: String.Encoding.utf8)
        }
        
        return nil
    }

4.示例

        let sign = YKEcdhSign()
            sign.generateKey()
            let enData =  sign.encryptedData(sourceData: originalData!, algorithm: SecKeyAlgorithm.eciesEncryptionStandardX963SHA512AESGCM)
            let string = sign.decryptedData(sourceData: enData!, algorithm: SecKeyAlgorithm.eciesEncryptionStandardX963SHA512AESGCM)
            print(string!)