browserify-hybrid-crypto/src/hybrid-decrypt.ts

TypeScript implementation Hybrid encryption and signing library built on Web Crypto (AES + RSA + HMAC).

import { importPrivateKey } from "./import-key";
import { HybridEncryption, HybridCryptoOptions } from "./interfaces";
import { getCryptoImpl } from "./utils";
import { getAesParams } from "./aes-params";

export async function hybridDecrypt(
  privateKeyPEM: string,
  {
    encryptedSessionKey,
    encryptedSigningKey,
    encryptedData,
    signature,
    iv,
  }: HybridEncryption,
  options: HybridCryptoOptions = {},
): Promise<string> {
  const crypto = getCryptoImpl();

  const { aesAlgorithm = "AES-GCM", hmacHash = "SHA-256" } = options;

  // Import private key
  const privateKey = await importPrivateKey(privateKeyPEM);

  // Decrypt the session key with the private key using RSA-OAEP
  const sessionKey = await crypto.subtle.decrypt(
    { name: "RSA-OAEP" },
    privateKey,
    encryptedSessionKey,
  );

  // Import the session key into a CryptoKey object for AES-GCM decryption
  const sessionCryptoKey = await crypto.subtle.importKey(
    "raw",
    sessionKey,
    { name: aesAlgorithm },
    false,
    ["decrypt"],
  );

  // Decrypt the signing key with the privateKey using RSA-OAEP
  const signingKey = await crypto.subtle.decrypt(
    { name: "RSA-OAEP" },
    privateKey,
    encryptedSigningKey,
  );

  // Import the signing key into a CryptoKey object for HMAC verification
  const signingCryptoKey = await crypto.subtle.importKey(
    "raw",
    signingKey,
    {
      name: "HMAC",
      hash: hmacHash,
    },
    false,
    ["verify"],
  );

  // Verify the signature of the encrypted data
  const isValidSignature = await crypto.subtle.verify(
    { name: "HMAC" },
    signingCryptoKey,
    signature,
    encryptedData,
  );

  if (!isValidSignature) {
    throw new Error("Signature verification failed");
  }

  // Get AES params and IV/counter for decryption
  const aesParams = getAesParams(aesAlgorithm, options, iv);

  // Decrypt the data with the session key using AES
  const decryptedData = await crypto.subtle.decrypt(
    aesParams.aesParams,
    sessionCryptoKey,
    encryptedData,
  );

  // Decode the decrypted data from ArrayBuffer to string
  return new TextDecoder().decode(decryptedData);
}