How to programmatically calculate Chrome extension ID?

Question

I\'m building an automated process to produce extensions. Is there a code example of calculating the extension-ID directly and entirely bypassing interaction with the browse

Answer 1

I was only able to find a related article with a Ruby fragment, and it's only available in the IA: http://web.archive.org/web/20120606044635/http://supercollider.dk/2010/01/calculating-chrome-extension-id-from-your-private-key-233

Important to know:

1. This depends on a DER-encoded public key (raw binary), not a PEM-encoded key (nice ASCII generated by base64-encoding the DER key).
2. The extension-IDs are base-16, but are encoded using [a-p] (called "mpdecimal"), rather than [0-9a-f].

Using a PEM-encoded public key, follow the following steps:

1. If your PEM-formatted public-key still has the header and footer and is split into multiple lines, reformat it by hand so that you have a single string of characters that excludes the header and footer, and runs together such that every line of the key wraps to the next.
2. Base64-decode the public key to render a DER-formatted public-key.
3. Generate a SHA256 hex-digest of the DER-formatted key.
4. Take the first 32-bytes of the hash. You will not need the rest.
5. For each character, convert it to base-10, and add the ASCII code for 'a'.

The following is a Python routine to do this:

import hashlib
from base64 import b64decode

def build_id(pub_key_pem):
    pub_key_der = b64decode(pub_key_pem)
    sha = hashlib.sha256(pub_key_der).hexdigest()
    prefix = sha[:32]

    reencoded = ""
    ord_a = ord('a')
    for old_char in prefix:
        code = int(old_char, 16)
        new_char = chr(ord_a + code)

        reencoded += new_char

    return reencoded

def main():
    pub_key = 'MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCjvF5pjuK8gRaw/2LoRYi37QqRd48B/FeO9yFtT6ueY84z/u0NrJ/xbPFc9OCGBi8RKIblVvcbY0ySGqdmp0QsUr/oXN0b06GL4iB8rMhlO082HhMzrClV8OKRJ+eJNhNBl8viwmtJs3MN0x9ljA4HQLaAPBA9a14IUKLjP0pWuwIDAQAB'

    id_ = build_id(pub_key)
    print(id_)

if __name__ == '__main__':
    main()

You're more than welcome to test this against an existing extension and its ID. To retrieve its PEM-formatted public-key:

1. Go into the list of your existing extensions in Chrome. Grab the extension-ID of one.
2. Find the directory where the extension is hosted. On my Windows 7 box, it is: C:\Users\AppData\Local\Google\Chrome\User Data\Default\Extensions
3. Grab the public-key from the manifest.json file under "key". Since the key is already ready to be base64-decoded, you can skip step (1) of the process.

The public-key in the example is from the "Chrome Reader" extension. Its extension ID is "lojpenhmoajbiciapkjkiekmobleogjc".

See also:

1. Google Chrome - Alphanumeric hashes to identify extensions
2. http://blog.roomanna.com/12-14-2010/getting-an-extensions-id