contains_similar method

[seisvelas]

It would be interesting to have a method "contains_similar". That would also catch something like f1owcrypt-security.com

Originally posted by @tomholub in https://github.com/FlowCrypt/flowcrypt-backend/pull/290#discussion_r582715348

[seisvelas]

Something like:

def contains_similar(domain1, domain2):
    small = min(domain1, domain2, key=len)
    big = max(domain1, domain2, key=len)

    for i in range(0, len(big) - len(small)):
        if looks_similar(small, big[i:i+len(small)]):
            return True

    return False

# Use like this
contains_similar('flowcrypt-security', 'f1owcrypt') == True

Haven't tried it out, just threw that together here in this comment (so probably glaring errors all over the place). I'll look at it more tomorrow.

Note - the for loop here increments the exponent of the time complexity. I'll perform some metrics to see how slow this is on big strings to see if it's realistic for running in production (don't want to harden our homograph defense only to open up an even more severe DoS vector)