From: David Kerkeslager <kerkeslager@gmail.com>
Date: Fri, 12 Feb 2021 19:30:56 +0000 (-0500)
Subject: Set 1 challenge 5
X-Git-Url: https://code.kerkeslager.com/?p=sandbox;a=commitdiff_plain;h=45ec9c36ab7241cee93e615b3c901b5b80aa7aff

Set 1 challenge 5
---

diff --git a/cryptopals-python/cryptopals.py b/cryptopals-python/cryptopals.py
index 56501a1..ee81112 100644
--- a/cryptopals-python/cryptopals.py
+++ b/cryptopals-python/cryptopals.py
@@ -32,6 +32,15 @@ with open('sample.txt','r') as sample_file:
 
 SAMPLE_FREQUENCIES = get_character_frequencies(sample_text)
 
+def encrypt_with_repeating_xor(plaintext, key):
+    plaintext_bytes = plaintext.encode('utf-8')
+    key_bytes = key.encode('utf-8')
+
+    return xor_bytes(
+        plaintext_bytes,
+        (key_bytes * ((len(plaintext_bytes) // len(key_bytes)) + 1))[:len(plaintext_bytes)],
+    )
+
 class Set1Challenge1Tests(unittest.TestCase):
     def test_converts_hex_to_base64(self):
         expected = 'SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t\n'
@@ -108,5 +117,15 @@ class Set1Challenge4Tests(unittest.TestCase):
 
         self.assertEqual(expected, actual)
 
+class Set1Challenge5Tests(unittest.TestCase):
+    def test_encrypts_with_repeating_xor(self):
+        plaintext = "Burning 'em, if you ain't quick and nimble\nI go crazy when I hear a cymbal"
+        key = 'ICE'
+
+        expected = '0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f'
+        actual = encrypt_with_repeating_xor(plaintext, key).hex()
+
+        self.assertEqual(expected, actual)
+
 if __name__ == '__main__':
     unittest.main()