# Key Agreement Using ECDH


For details about the algorithm specifications, see [ECDH](crypto-key-agreement-overview.md#ecdh).


## How to Develop

1. Use [cryptoFramework.createAsyKeyGenerator](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreateasykeygenerator), [AsyKeyGenerator.generateKeyPair](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#generatekeypair-1), and [AsyKeyGenerator.convertKey](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#convertkey-3) to generate a 256-bit ECC key pair (**KeyPair**).
   
   In addition to the example in this topic, [ECC](crypto-asym-key-generation-conversion-spec.md#ecc) and [Randomly Generating an Asymmetric Key Pair](crypto-generate-asym-key-pair-randomly.md) may help you better understand how to generate an ECC asymmetric key pair. Note that the input parameters in the reference documents may be different from those in the example below.

2. Use [cryptoFramework.createKeyAgreement](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreatekeyagreement) with the string parameter **'ECC256'** to create a 256-bit ECC key agreement (**KeyAgreement**) instance.

3. Use [KeyAgreement.generateSecret](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#generatesecret-1) to perform key agreement with the specified private key (**KeyPair.priKey**) and public key (**KeyPair.pubKey**), and return the shared secret.

- Example: Perform key agreement using **await**.

  ```ts
  import { cryptoFramework } from '@kit.CryptoArchitectureKit';

  async function ecdhAwait() {
    // The public and private key pair data is transferred from an external system.
    let pubKeyArray = new Uint8Array([48, 89, 48, 19, 6, 7, 42, 134, 72, 206, 61, 2, 1, 6, 8, 42, 134, 72, 206, 61, 3, 1, 7, 3, 66, 0, 4, 83, 96, 142, 9, 86, 214, 126, 106, 247, 233, 92, 125, 4, 128, 138, 105, 246, 162, 215, 71, 81, 58, 202, 121, 26, 105, 211, 55, 130, 45, 236, 143, 55, 16, 248, 75, 167, 160, 167, 106, 2, 152, 243, 44, 68, 66, 0, 167, 99, 92, 235, 215, 159, 239, 28, 106, 124, 171, 34, 145, 124, 174, 57, 92]);
    let priKeyArray = new Uint8Array([48, 49, 2, 1, 1, 4, 32, 115, 56, 137, 35, 207, 0, 60, 191, 90, 61, 136, 105, 210, 16, 27, 4, 171, 57, 10, 61, 123, 40, 189, 28, 34, 207, 236, 22, 45, 223, 10, 189, 160, 10, 6, 8, 42, 134, 72, 206, 61, 3, 1, 7]);
    let eccGen = cryptoFramework.createAsyKeyGenerator('ECC256');
    // Key pair A transferred from an external system.
    let keyPairA = await eccGen.convertKey({ data: pubKeyArray }, { data: priKeyArray });
    // Key pair B generated internally.
    let keyPairB = await eccGen.generateKeyPair();
    let eccKeyAgreement = cryptoFramework.createKeyAgreement('ECC256');
    // Use the public key of A and the private key of B to perform key agreement.
    let secret1 = await eccKeyAgreement.generateSecret(keyPairB.priKey, keyPairA.pubKey);
    // Use the private key of A and the public key of B to perform key agreement.
    let secret2 = await eccKeyAgreement.generateSecret(keyPairA.priKey, keyPairB.pubKey);
    // The two key agreement results should be the same.
    if (secret1.data.toString() == secret2.data.toString()) {
      console.info('ecdh success');
      console.info('ecdh output is ' + secret1.data);
    } else {
      console.error('ecdh result is not equal');
    }
  }
  ```

- Example (using synchronous APIs):

  ```ts
  import { cryptoFramework } from '@kit.CryptoArchitectureKit';

  function ecdhAwait() {
    // The public and private key pair data is transferred from an external system.
    let pubKeyArray = new Uint8Array([48, 89, 48, 19, 6, 7, 42, 134, 72, 206, 61, 2, 1, 6, 8, 42, 134, 72, 206, 61, 3, 1, 7, 3, 66, 0, 4, 83, 96, 142, 9, 86, 214, 126, 106, 247, 233, 92, 125, 4, 128, 138, 105, 246, 162, 215, 71, 81, 58, 202, 121, 26, 105, 211, 55, 130, 45, 236, 143, 55, 16, 248, 75, 167, 160, 167, 106, 2, 152, 243, 44, 68, 66, 0, 167, 99, 92, 235, 215, 159, 239, 28, 106, 124, 171, 34, 145, 124, 174, 57, 92]);
    let priKeyArray = new Uint8Array([48, 49, 2, 1, 1, 4, 32, 115, 56, 137, 35, 207, 0, 60, 191, 90, 61, 136, 105, 210, 16, 27, 4, 171, 57, 10, 61, 123, 40, 189, 28, 34, 207, 236, 22, 45, 223, 10, 189, 160, 10, 6, 8, 42, 134, 72, 206, 61, 3, 1, 7]);
    let eccGen = cryptoFramework.createAsyKeyGenerator('ECC256');
    // Key pair A transferred from an external system.
    let keyPairA = eccGen.convertKeySync({ data: pubKeyArray }, { data: priKeyArray });
    // Key pair B generated internally.
    let keyPairB = eccGen.generateKeyPairSync();
    let eccKeyAgreement = cryptoFramework.createKeyAgreement('ECC256');
    // Use the public key of A and the private key of B to perform key agreement.
    let secret1 = eccKeyAgreement.generateSecretSync(keyPairB.priKey, keyPairA.pubKey);
    // Use the private key of A and the public key of B to perform key agreement.
    let secret2 = eccKeyAgreement.generateSecretSync(keyPairA.priKey, keyPairB.pubKey);
    // The two key agreement results should be the same.
    if (secret1.data.toString() == secret2.data.toString()) {
      console.info('ecdh success');
      console.info('ecdh output is ' + secret1.data);
    } else {
      console.error('ecdh result is not equal');
    }
  }
  ```