Question

Google Chrome is using alpha numeric hashes as identifiers for the Chrome extensions. For eg. “ajpgkpeckebdhofmmjfgcjjiiejpodla” is the identifier for XMarks Bookmark Sync extension.

Which algorithm is in use here to generate such strings? How are they ensuring uniqueness?

Answer 1

Chromium generates the id via public key. If you use the extension gallery, they handle all that for you.

From the source:

bool Extension::GenerateId(const std::string& input, std::string* output) {
  CHECK(output);
  if (input.length() == 0)
    return false;

  const uint8* ubuf = reinterpret_cast<const unsigned char*>(input.data());
  SHA256Context ctx;
  SHA256_Begin(&ctx);
  SHA256_Update(&ctx, ubuf, input.length());
  uint8 hash[Extension::kIdSize];
  SHA256_End(&ctx, hash, NULL, sizeof(hash));
  *output = StringToLowerASCII(HexEncode(hash, sizeof(hash)));
  ConvertHexadecimalToIDAlphabet(output);

  return true;
}

Take a look at extension.cc file it has more detailed information such as generating the .pem file exncoding/decoding, etc.