I want to log script hashes to implement content security policy. I have been able to generate the hash in python with the following code:

import hashlib
import base64

string='''
//<![CDATA[
var theForm = document.forms['ctl00'];
if (!theForm) {
    theForm = document.ctl00;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
'''
# encode as UTF-8
string_UTF8 = string.encode('utf-8')

# hash the message
hash_string = hashlib.sha256(string_UTF8).digest()

# base64 encode
result = base64.b64encode(hash_string)

print('sha256-' + result.decode('utf-8'))

How can I do this with Javascript?

I want to log script hashes to implement content security policy. I have been able to generate the hash in python with the following code:

import hashlib
import base64

string='''
//<![CDATA[
var theForm = document.forms['ctl00'];
if (!theForm) {
    theForm = document.ctl00;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
'''
# encode as UTF-8
string_UTF8 = string.encode('utf-8')

# hash the message
hash_string = hashlib.sha256(string_UTF8).digest()

# base64 encode
result = base64.b64encode(hash_string)

print('sha256-' + result.decode('utf-8'))

How can I do this with Javascript?

• javascript
• python
• base64
• content-security-policy
• sha256

• take a look here: stackoverflow./questions/37128276/… – Binzari Catalin Commented Oct 7, 2021 at 14:55
• That looks like it would work, but I specifically want to do this on the fly, in a web browser, for scripts on the loaded page. – cmdln Commented Oct 7, 2021 at 18:02

2 Answers 2

const string = `
//<![CDATA[
var theForm = document.forms['ctl00'];
if (!theForm) {
    theForm = document.ctl00;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
`

async function hashFromString(string) {
    const hash = await crypto.subtle.digest("SHA-256", (new TextEncoder()).encode(string))
    return "sha256-" + btoa(String.fromCharCode(...new Uint8Array(hash)))
}

hashFromString(string).then(console.log)

Edit: I realize now that while not stated in your question it's likely that you are using Node.js therefor this answer that uses browser APIs may be of less use.

I ended up using this JQuery plugin https://github./angeal185/jquery-hash The following code gets the correct answer:

<script>
  var s = "\n//<![CDATA[\nvar theForm = document.forms['ctl00'];\nif (!theForm) {\n    theForm = document.ctl00;\n}\nfunction __doPostBack(eventTarget, eventArgument) {\n    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {\n        theForm.__EVENTTARGET.value = eventTarget;\n        theForm.__EVENTARGUMENT.value = eventArgument;\n        theForm.submit();\n    }\n}\n//]]>\n"
  $.hash(s, '256', 'base64',function(i){
  console.log(i)
  });
</script>