1# Key Agreement Using DH
2
3
4For details about the algorithm specifications, see [DH](crypto-key-agreement-overview.md#dh).
5
6
7## How to Develop
8
91. Use [cryptoFramework.createAsyKeyGenerator](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreateasykeygenerator) and [AsyKeyGenerator.generateKeyPair](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#generatekeypair-1) to generate a DH asymmetric key pair (**KeyPair**) with the named DH group **modp1536**.
10   In addition to the example in this topic, [DH](crypto-asym-key-generation-conversion-spec.md#dh) and [Randomly Generating an Asymmetric Key Pair](crypto-generate-asym-key-pair-randomly.md) may help you better understand how to generate a DH asymmetric key pair. Note that the input parameters in the reference documents may be different from those in the example below.
11
122. Use [cryptoFramework.createKeyAgreement](../../reference/apis-crypto-architecture-kit/js-apis-cryptoFramework.md#cryptoframeworkcreatekeyagreement) with the string parameter **'DH_modp1536'** to create a key agreement (**KeyAgreement**) instance.
13
143. 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.
15
16- Example: Perform key agreement using **await**.
17
18  ```ts
19  import { cryptoFramework } from '@kit.CryptoArchitectureKit';
20
21  async function dhAwait() {
22    let keyGen = cryptoFramework.createAsyKeyGenerator('DH_modp1536');
23    // Randomly generate public-private key pair A.
24    let keyPairA = await keyGen.generateKeyPair();
25    // Randomly generate public-private key pair B with the same specifications.
26    let keyPairB = await keyGen.generateKeyPair();
27    let keyAgreement = cryptoFramework.createKeyAgreement('DH_modp1536');
28    // Use the public key of A and the private key of B to perform key agreement.
29    let secret1 = await keyAgreement.generateSecret(keyPairB.priKey, keyPairA.pubKey);
30    // Use the private key of A and the public key of B to perform key agreement.
31    let secret2 = await keyAgreement.generateSecret(keyPairA.priKey, keyPairB.pubKey);
32    // The two key agreement results should be the same.
33    if (secret1.data.toString() == secret2.data.toString()) {
34      console.info('DH success');
35      console.info('DH output is ' + secret1.data);
36    } else {
37      console.error('DH result is not equal');
38    }
39  }
40  ```
41
42- Example (using synchronous APIs):
43
44  ```ts
45  import { cryptoFramework } from '@kit.CryptoArchitectureKit';
46
47  function dhAwait() {
48    let keyGen = cryptoFramework.createAsyKeyGenerator('DH_modp1536');
49    // Randomly generate public-private key pair A.
50    let keyPairA = keyGen.generateKeyPairSync();
51    // Randomly generate public-private key pair B with the same specifications.
52    let keyPairB = keyGen.generateKeyPairSync();
53    let keyAgreement = cryptoFramework.createKeyAgreement('DH_modp1536');
54    // Use the public key of A and the private key of B to perform key agreement.
55    let secret1 = keyAgreement.generateSecretSync(keyPairB.priKey, keyPairA.pubKey);
56    // Use the private key of A and the public key of B to perform key agreement.
57    let secret2 = keyAgreement.generateSecretSync(keyPairA.priKey, keyPairB.pubKey);
58    // The two key agreement results should be the same.
59    if (secret1.data.toString() == secret2.data.toString()) {
60      console.info('DH success');
61      console.info('DH output is ' + secret1.data);
62    } else {
63      console.error('DH result is not equal');
64    }
65  }
66  ```
67