harmony 鸿蒙Converting Compressed or Uncompressed ECC Point Data (ArkTS)

2025-06-12
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Converting Compressed or Uncompressed ECC Point Data (ArkTS)

You can convert compressed or uncompressed point data into a Point object for generating a key object, or convert a Point object into compressed or uncompressed point data. For details about the ECC algorithm specifications, see ECC. You can pass in the string parameter format to specify the format of the point data to obtain. To obtain compressed point data, set format to COMPRESSED. To obtain uncompressed point data, set format to UNCOMPRESSED.

Converting Uncompressed Point Data into Compressed Point Data

Call ECCKeyUtil.convertPoint to convert uncompressed ECC point data of the Uint8Array type into a Point object.
Call ECCKeyUtil.getEncodedPoint to obtain compressed point data.

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

function eccPointUncompressedToCompressed() {
  let pkData = new Uint8Array([4, 143, 39, 57, 249, 145, 50, 63, 222, 35, 70, 178, 121, 202, 154, 21, 146, 129, 75, 76, 63, 8, 195, 157, 111, 40, 217, 215, 148, 120, 224, 205, 82, 83, 92, 185, 21, 211, 184, 5, 19, 114, 33, 86, 85, 228, 123, 242, 206, 200, 98, 178, 184, 130, 35, 232, 45, 5, 202, 189, 11, 46, 163, 156, 152]);
  let returnPoint = cryptoFramework.ECCKeyUtil.convertPoint('NID_brainpoolP256r1', pkData);
  console.info('convertPoint success');
  let returnData = cryptoFramework.ECCKeyUtil.getEncodedPoint('NID_brainpoolP256r1', returnPoint, 'COMPRESSED');
  console.info('returnData: ' + returnData); // returnData is 2,143,39,57,249,145,50,63,222,35,70,178,121,202,154,21,146,129,75,76,63,8,195,157,111,40,217,215,148,120,224,205,82 (the prefix of the compressed point data is 02 because y is an even number). 
}

Converting Compressed Point Data into a Key Object

Call ECCKeyUtil.convertPoint to convert the compressed ECC point data of the Uint8Array type into a Point object.
Call ECCKeyUtil.genECCCommonParamsSpec with the curve name set to NID_brainpoolP256r1 to generate the common key parameters for the ECC key pair.
Construct a ECCPubKeySpec object to specify the parameters for the ECC public key. ECCPubKeySpec is a child class of AsyKeySpec. Set algName to ECC, specify AsyKeySpecType.PUBLIC_KEY_SPEC, and set pk to the Point object obtained in step 1.
Call createAsyKeyGeneratorBySpec with the public key parameters to create an asymmetric key generator (AsyKeyGeneratorBySpec) object.
Call AsyKeyGeneratorBySpec.generatePubKey to generate the public key.
Call ECCKeyUtil.getEncodedPoint to obtain uncompressed point data.
Call PubKey.getAsyKeySpec to obtain the x coordinate of the ECC public key pk.

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

async function eccPointCompressedToPoint() {
  let pkData = new Uint8Array([2, 143, 39, 57, 249, 145, 50, 63, 222, 35, 70, 178, 121, 202, 154, 21, 146, 129, 75, 76, 63, 8, 195, 157, 111, 40, 217, 215, 148, 120, 224, 205, 82]);
  let returnPoint = cryptoFramework.ECCKeyUtil.convertPoint('NID_brainpoolP256r1', pkData);
  console.info('convertPoint success');
  let eccCommonParamsSpec = cryptoFramework.ECCKeyUtil.genECCCommonParamsSpec('NID_brainpoolP256r1');
  let eccPubKeySpec: cryptoFramework.ECCPubKeySpec = {
    algName: "ECC",
    specType: cryptoFramework.AsyKeySpecType.PUBLIC_KEY_SPEC,
    params: eccCommonParamsSpec,
    pk: returnPoint
  };
  let generatorBySpec = cryptoFramework.createAsyKeyGeneratorBySpec(eccPubKeySpec);
  let pubKey = await generatorBySpec.generatePubKey();
  let returnData = cryptoFramework.ECCKeyUtil.getEncodedPoint('NID_brainpoolP256r1', returnPoint, 'UNCOMPRESSED');
  console.info('returnData: ' + returnData); // 4,143,39,57,249,145,50,63,222,35,70,178,121,202,154,21,146,129,75,76,63,8,195,157,111,40,217,215,148,120,224,205,82,83,92,185,21,211,184,5,19,114,33,86,85,228,123,242,206,200,98,178,184,130,35,232,45,5,202,189,11,46,163,156,152
  let eccPkX = pubKey.getAsyKeySpec(cryptoFramework.AsyKeySpecItem.ECC_PK_X_BN);
  console.info('returnPoint x data: ' + returnPoint.x); // 64750044510792891439269945828433327517677381559622384455951527515863444933970
  console.info('ECC_PK_X_BN: ' + eccPkX); // 64750044510792891439269945828433327517677381559622384455951527515863444933970
}