Obtaining a Public Key from a Private Key (ArkTS)

Since API version 23, the algorithm library supports obtaining a public key based on a private key.

The following uses RSA as an example to describe how to obtain a public key based on a private key.

For details about the algorithm specifications, see RSA.

How to Develop

Call cryptoFramework.createAsyKeyGenerator with the string parameter 'RSA1024' to create an asymmetric key generator (AsyKeyGenerator) for a 1024-bit RSA key with two primes.

The default number of primes for creating an RSA asymmetric key is 2. The PRIMES_2 parameter is omitted in the string parameter here.
Call AsyKeyGenerator.generateKeyPair to randomly generate an asymmetric key pair (KeyPair).

The KeyPair object includes a public key (PubKey) and a private key (PriKey).
Call PubKey.getEncoded to obtain the binary data of the public key object in KeyPair.
Call PriKey.getPubKey to obtain the public key object PubKey from the private key.
Call PubKey.getEncoded to obtain the binary data of the PubKey object.
Compares the binary data of the two public key objects.

Example: Generate an RSA key pair asynchronously (by calling getPubKey):

import { cryptoFramework } from '@kit.CryptoArchitectureKit';
import { buffer } from '@kit.ArkTS';

function compareUint8Array(a: Uint8Array, b: Uint8Array): boolean {
  let buf1 = buffer.from(a);
  let buf2 = buffer.from(b);
  if (buf1.compare(buf2, 0, b.length, 0, a.length) == 0) {
      return true;
  } else {
      return false;
  }
}

async function prikeyGetPubKeyAsync() {
  let skData =
    new Uint8Array([48, 130, 2, 119, 2, 1, 0, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 1, 5, 0, 4, 130, 2, 97, 48,
      130, 2, 93, 2, 1, 0, 2, 129, 129, 0, 199, 32, 218, 8, 4, 63, 103, 229, 64, 128, 83, 31, 23, 156, 30, 168, 101, 22,
      80, 100, 197, 243, 217, 60, 127, 110, 127, 242, 8, 251, 87, 127, 235, 38, 226, 149, 149, 108, 54, 202, 53, 1, 21,
      91, 118, 246, 97, 93, 147, 117, 162, 71, 215, 70, 9, 175, 205, 241, 230, 187, 64, 170, 154, 67, 67, 254, 71, 1,
      114, 10, 91, 195, 34, 199, 85, 172, 255, 87, 95, 159, 43, 117, 73, 73, 199, 97, 198, 117, 217, 7, 188, 196, 30,
      248, 9, 181, 150, 243, 41, 145, 91, 8, 226, 161, 251, 12, 120, 28, 36, 146, 3, 196, 48, 243, 136, 201, 207, 131,
      171, 22, 15, 7, 12, 172, 135, 196, 30, 93, 2, 3, 1, 0, 1, 2, 129, 128, 109, 100, 83, 194, 225, 170, 127, 134, 6,
      184, 56, 113, 181, 67, 179, 231, 232, 152, 168, 147, 163, 215, 193, 56, 165, 252, 235, 86, 232, 174, 67, 52, 103,
      215, 149, 212, 125, 32, 212, 188, 162, 255, 180, 94, 233, 236, 146, 50, 153, 6, 159, 158, 253, 217, 97, 10, 238,
      133, 124, 174, 211, 232, 165, 19, 100, 186, 218, 62, 46, 124, 30, 19, 251, 3, 206, 105, 255, 236, 224, 178, 148,
      103, 44, 132, 71, 83, 28, 221, 27, 189, 72, 44, 59, 253, 139, 232, 234, 14, 112, 121, 43, 142, 193, 179, 140, 200,
      97, 234, 110, 63, 205, 24, 88, 116, 86, 184, 8, 19, 254, 204, 77, 84, 66, 238, 240, 69, 72, 21, 2, 65, 0, 233,
      103, 239, 11, 215, 10, 103, 66, 46, 155, 193, 79, 37, 64, 90, 12, 167, 189, 129, 8, 131, 94, 195, 8, 210, 236, 87,
      158, 140, 2, 82, 105, 80, 253, 13, 26, 140, 202, 194, 117, 59, 57, 197, 108, 50, 20, 46, 89, 248, 132, 120, 30,
      149, 180, 135, 134, 196, 156, 160, 123, 38, 253, 15, 7, 2, 65, 0, 218, 103, 122, 117, 154, 149, 213, 110, 24, 149,
      175, 208, 136, 249, 88, 91, 89, 180, 30, 243, 69, 130, 97, 252, 177, 216, 55, 46, 67, 15, 124, 56, 113, 57, 242,
      233, 185, 193, 254, 218, 76, 165, 184, 16, 109, 190, 93, 195, 227, 37, 58, 110, 243, 142, 152, 252, 226, 91, 59,
      145, 218, 35, 106, 123, 2, 65, 0, 210, 131, 88, 58, 32, 144, 148, 131, 63, 144, 97, 112, 165, 211, 125, 164, 110,
      97, 224, 16, 50, 148, 116, 105, 239, 251, 20, 39, 190, 117, 149, 168, 193, 80, 10, 210, 136, 107, 147, 169, 178,
      106, 47, 162, 159, 36, 78, 141, 253, 52, 85, 54, 152, 165, 131, 154, 204, 151, 203, 178, 103, 126, 212, 95, 2, 65,
      0, 193, 254, 80, 3, 205, 255, 112, 200, 142, 5, 199, 88, 207, 145, 203, 45, 185, 12, 8, 193, 196, 231, 254, 233,
      89, 126, 215, 228, 187, 164, 49, 142, 96, 228, 60, 35, 230, 223, 173, 227, 113, 89, 113, 153, 6, 33, 165, 95, 173,
      143, 15, 204, 37, 130, 111, 217, 143, 165, 193, 207, 215, 150, 197, 169, 2, 64, 7, 37, 152, 14, 232, 168, 102,
      169, 167, 97, 161, 33, 86, 178, 77, 140, 12, 114, 78, 129, 47, 103, 87, 217, 177, 80, 156, 91, 240, 149, 254, 90,
      69, 232, 10, 56, 232, 63, 59, 148, 254, 101, 63, 146, 66, 96, 25, 31, 37, 154, 77, 145, 201, 213, 122, 245, 90,
      251, 219, 42, 131, 248, 148, 151
      ])
  let expectPkdata =
    new Uint8Array([48, 129, 159, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 1, 5, 0, 3, 129, 141, 0, 48, 129, 137,
      2, 129, 129, 0, 199, 32, 218, 8, 4, 63, 103, 229, 64, 128, 83, 31, 23, 156, 30, 168, 101, 22, 80, 100, 197, 243,
      217, 60, 127, 110, 127, 242, 8, 251, 87, 127, 235, 38, 226, 149, 149, 108, 54, 202, 53, 1, 21, 91, 118, 246, 97,
      93, 147, 117, 162, 71, 215, 70, 9, 175, 205, 241, 230, 187, 64, 170, 154, 67, 67, 254, 71, 1, 114, 10, 91, 195,
      34, 199, 85, 172, 255, 87, 95, 159, 43, 117, 73, 73, 199, 97, 198, 117, 217, 7, 188, 196, 30, 248, 9, 181, 150,
      243, 41, 145, 91, 8, 226, 161, 251, 12, 120, 28, 36, 146, 3, 196, 48, 243, 136, 201, 207, 131, 171, 22, 15, 7, 12,
      172, 135, 196, 30, 93, 2, 3, 1, 0, 1
      ])
  let skDataBlob: cryptoFramework.DataBlob = { data: skData };
  let rsaGenerator = cryptoFramework.createAsyKeyGenerator('RSA1024');
  try {
    let keyPair = rsaGenerator.convertKeySync(null, skDataBlob);
    let priKey = keyPair.priKey;
    let pubkey = await priKey.getPubKey();
    let pkBlob = pubkey.getEncoded();
    console.info('pk1 bin data: ' + pkBlob.data);
    let ret: boolean = compareUint8Array(pkBlob.data, expectPkdata);
    console.info('result: ' + ret);
  } catch (e) {
    console.error(`get pubkey from prikey failed: errCode: ${e.code}, message: ${e.message}`);
  }
}

Example: Generate an RSA key pair synchronously (by calling getPubKeySync):

import { cryptoFramework } from '@kit.CryptoArchitectureKit';
import { buffer } from '@kit.ArkTS';

function compareUint8Array(a: Uint8Array, b: Uint8Array): boolean {
  let buf1 = buffer.from(a);
  let buf2 = buffer.from(b);
  if (buf1.compare(buf2, 0, b.length, 0, a.length) == 0) {
      return true;
  } else {
      return false;
  }
}

function generateAsyKey() {
  let skData =
    new Uint8Array([48, 130, 2, 119, 2, 1, 0, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 1, 5, 0, 4, 130, 2, 97, 48,
      130, 2, 93, 2, 1, 0, 2, 129, 129, 0, 199, 32, 218, 8, 4, 63, 103, 229, 64, 128, 83, 31, 23, 156, 30, 168, 101, 22,
      80, 100, 197, 243, 217, 60, 127, 110, 127, 242, 8, 251, 87, 127, 235, 38, 226, 149, 149, 108, 54, 202, 53, 1, 21,
      91, 118, 246, 97, 93, 147, 117, 162, 71, 215, 70, 9, 175, 205, 241, 230, 187, 64, 170, 154, 67, 67, 254, 71, 1,
      114, 10, 91, 195, 34, 199, 85, 172, 255, 87, 95, 159, 43, 117, 73, 73, 199, 97, 198, 117, 217, 7, 188, 196, 30,
      248, 9, 181, 150, 243, 41, 145, 91, 8, 226, 161, 251, 12, 120, 28, 36, 146, 3, 196, 48, 243, 136, 201, 207, 131,
      171, 22, 15, 7, 12, 172, 135, 196, 30, 93, 2, 3, 1, 0, 1, 2, 129, 128, 109, 100, 83, 194, 225, 170, 127, 134, 6,
      184, 56, 113, 181, 67, 179, 231, 232, 152, 168, 147, 163, 215, 193, 56, 165, 252, 235, 86, 232, 174, 67, 52, 103,
      215, 149, 212, 125, 32, 212, 188, 162, 255, 180, 94, 233, 236, 146, 50, 153, 6, 159, 158, 253, 217, 97, 10, 238,
      133, 124, 174, 211, 232, 165, 19, 100, 186, 218, 62, 46, 124, 30, 19, 251, 3, 206, 105, 255, 236, 224, 178, 148,
      103, 44, 132, 71, 83, 28, 221, 27, 189, 72, 44, 59, 253, 139, 232, 234, 14, 112, 121, 43, 142, 193, 179, 140, 200,
      97, 234, 110, 63, 205, 24, 88, 116, 86, 184, 8, 19, 254, 204, 77, 84, 66, 238, 240, 69, 72, 21, 2, 65, 0, 233,
      103, 239, 11, 215, 10, 103, 66, 46, 155, 193, 79, 37, 64, 90, 12, 167, 189, 129, 8, 131, 94, 195, 8, 210, 236, 87,
      158, 140, 2, 82, 105, 80, 253, 13, 26, 140, 202, 194, 117, 59, 57, 197, 108, 50, 20, 46, 89, 248, 132, 120, 30,
      149, 180, 135, 134, 196, 156, 160, 123, 38, 253, 15, 7, 2, 65, 0, 218, 103, 122, 117, 154, 149, 213, 110, 24, 149,
      175, 208, 136, 249, 88, 91, 89, 180, 30, 243, 69, 130, 97, 252, 177, 216, 55, 46, 67, 15, 124, 56, 113, 57, 242,
      233, 185, 193, 254, 218, 76, 165, 184, 16, 109, 190, 93, 195, 227, 37, 58, 110, 243, 142, 152, 252, 226, 91, 59,
      145, 218, 35, 106, 123, 2, 65, 0, 210, 131, 88, 58, 32, 144, 148, 131, 63, 144, 97, 112, 165, 211, 125, 164, 110,
      97, 224, 16, 50, 148, 116, 105, 239, 251, 20, 39, 190, 117, 149, 168, 193, 80, 10, 210, 136, 107, 147, 169, 178,
      106, 47, 162, 159, 36, 78, 141, 253, 52, 85, 54, 152, 165, 131, 154, 204, 151, 203, 178, 103, 126, 212, 95, 2, 65,
      0, 193, 254, 80, 3, 205, 255, 112, 200, 142, 5, 199, 88, 207, 145, 203, 45, 185, 12, 8, 193, 196, 231, 254, 233,
      89, 126, 215, 228, 187, 164, 49, 142, 96, 228, 60, 35, 230, 223, 173, 227, 113, 89, 113, 153, 6, 33, 165, 95, 173,
      143, 15, 204, 37, 130, 111, 217, 143, 165, 193, 207, 215, 150, 197, 169, 2, 64, 7, 37, 152, 14, 232, 168, 102,
      169, 167, 97, 161, 33, 86, 178, 77, 140, 12, 114, 78, 129, 47, 103, 87, 217, 177, 80, 156, 91, 240, 149, 254, 90,
      69, 232, 10, 56, 232, 63, 59, 148, 254, 101, 63, 146, 66, 96, 25, 31, 37, 154, 77, 145, 201, 213, 122, 245, 90,
      251, 219, 42, 131, 248, 148, 151
    ])
  let expectPkdata =
    new Uint8Array([48, 129, 159, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 1, 5, 0, 3, 129, 141, 0, 48, 129, 137,
      2, 129, 129, 0, 199, 32, 218, 8, 4, 63, 103, 229, 64, 128, 83, 31, 23, 156, 30, 168, 101, 22, 80, 100, 197, 243,
      217, 60, 127, 110, 127, 242, 8, 251, 87, 127, 235, 38, 226, 149, 149, 108, 54, 202, 53, 1, 21, 91, 118, 246, 97,
      93, 147, 117, 162, 71, 215, 70, 9, 175, 205, 241, 230, 187, 64, 170, 154, 67, 67, 254, 71, 1, 114, 10, 91, 195,
      34, 199, 85, 172, 255, 87, 95, 159, 43, 117, 73, 73, 199, 97, 198, 117, 217, 7, 188, 196, 30, 248, 9, 181, 150,
      243, 41, 145, 91, 8, 226, 161, 251, 12, 120, 28, 36, 146, 3, 196, 48, 243, 136, 201, 207, 131, 171, 22, 15, 7, 12,
      172, 135, 196, 30, 93, 2, 3, 1, 0, 1
    ])
  let skDataBlob: cryptoFramework.DataBlob = { data: skData };
  let rsaGenerator = cryptoFramework.createAsyKeyGenerator('RSA1024');
  try {
    let keyPair = rsaGenerator.convertKeySync(null, skDataBlob);
    let priKey = keyPair.priKey;
    let pubkey = priKey.getPubKeySync();
    let pkBlob = pubkey.getEncoded();
    console.info('pk1 bin data: ' + pkBlob.data);
    let ret: boolean = compareUint8Array(pkBlob.data, expectPkdata);
    console.info('result: ' + ret);
  } catch (e) {
    console.error(`get pubkey from prikey failed: errCode: ${e.code}, message: ${e.message}`);
  }
}