The implementation of DeviceFingerprint differs from the spec

[ghost]

https://github.com/cryptocat/cryptocat/blob/master/src/js/omemo.js#L590-L597

			var h = '';
			var i = 0;
			for (i = 0; i < username.length; i += 1) {
				h += ProScript.encoding.a2h(username);
			}
			for (i = 0; i < deviceName.length; i += 1) {
				h += ProScript.encoding.a2h(deviceName[i]);
			}

According to https://crypto.cat/security.html, username will be used only once in a calculation of device fingerprint. But actually, Cryptocat.OMEMO.deviceFingerprint() concatenates an entire username multiple times.

This implementation is equivalent to:

DeviceFingerprint = SHA256(
	deviceId                ||
	SHA256(
		username.repeat(username.length)   ||
		deviceName ||
		deviceIcon
	)                       ||
	deviceIdentityKeyPublic
).HexString().First32Characters()

[nadimkobeissi]

That's an implementation bug, and quite a silly one at that. Thanks for catching it.