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Challenge 83: Signature Validation

curriculum/challenges/english/blocks/daily-coding-challenges-python/68e39ed6106dac2f0a98fd65.md

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--description--

Given a message string, a secret key string, and a signature number, determine if the signature is valid using this encoding method:

  • Letters in the message and secret key have these values:
    • a to z have values 1 to 26 respectively.
    • A to Z have values 27 to 52 respectively.
  • All other characters have no value.
  • Compute the signature by taking the sum of the message plus the sum of the secret key.

For example, given the message "foo" and the secret key "bar", the signature would be 57:

md
f (6) + o (15) + o (15) = 36
b (2) + a (1) + r (18) = 21
36 + 21 = 57

Check if the computed signature matches the provided signature.

--hints--

verify("foo", "bar", 57) should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("foo", "bar", 57), True)`)
}})

verify("foo", "bar", 54) should return False.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("foo", "bar", 54), False)`)
}})

verify("freeCodeCamp", "Rocks", 238) should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("freeCodeCamp", "Rocks", 238), True)`)
}})

verify("Is this valid?", "No", 210) should return False.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("Is this valid?", "No", 210), False)`)
}})

verify("Is this valid?", "Yes", 233) should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("Is this valid?", "Yes", 233), True)`)
}})

verify("Check out the freeCodeCamp podcast,", "in the mobile app", 514) should return True.

js
({test: () => { runPython(`
from unittest import TestCase
TestCase().assertIs(verify("Check out the freeCodeCamp podcast,", "in the mobile app", 514), True)`)
}})

--seed--

--seed-contents--

py
def verify(message, key, signature):

    return message

--solutions--

py
def verify(message, key, signature):
    def charValue(ch) -> int:
        if 'a' <= ch <= 'z':
            return ord(ch) - ord('a') + 1
        elif 'A' <= ch <= 'Z':
            return ord(ch) - ord('A') + 27
        else:
            return 0

    def compute_sum(s):
        return sum(charValue(ch) for ch in s)

    total = compute_sum(message) + compute_sum(key)
    return total == signature