> single_byte_xor( b"$'&!", 69)ī'abcd' Deciphering without the encryption key Since encryption and decryption both have an exact same implementation - we pass the ciphertext to the function single_byte_xor, defined above, to get the original message back. we iterate through the encrypted message bytewise and XOR each byte with the encryption key - the resultant will be the original message. XOR has a property - if a = b ^ c then b = a ^ c, hence the decryption process is exactly the same as the encryption i.e. the encrypted message is $'&!.ĭecryption is the process of extracting the original message from the encrypted ciphertext given the encryption key. Hence when abcd is encrypted using single-byte XOR cipher and encryption key 69, the resultant ciphertext i.e. ASCII value is 97 which when XORed with 69 results in 36 whose character equivalent is $, similarly for b the encrypted byte is ', for c it is & and for d it is !. """ return bytes()Īs an example, we can try to encrypt the plain text - abcd - with encryption key 69 and as per the algorithm, we perform XOR bytewise on the given plain text. XOR of all the bytes and the `key` and returns the resultant. In range [0, 256) the function encrypts the text by performing def single_byte_xor (text: bytes, key: int) -> bytes: """Given a plain text `text` as bytes and an encryption key `key` as a byte Following is the python-based implementation of the encryption process. These encrypted bytes need not be among the usual printable characters and should ideally be interpreted as a stream of bytes. EncryptionĪs part of the encryption process, the original message is iterated bytewise and every single byte b is XORed with the encryption key key and the resultant stream of bytes is again translated back as characters and sent to the other party. Now we take a detailed look at how the encryption and decryption processes look like for this cipher. The Single-byte XOR cipher algorithm works with an encryption key of size 1 byte - which means the encryption key could be one of the possible 256 values of a byte. The problem statement, defined above, is based on Cryptopals Set 1 Challenge 3. In this essay, we will work with a very simple cipher (encryption algorithm) that uses an encryption key with a size of one byte, and try to decipher the ciphered text and retrieve the original message without knowing the encryption key. Usually, this depends on the number of bits in the key - bigger the key, the longer it takes to decrypt the enciphered data. The strength of an encryption algorithm is determined by how hard it would be to extract the original message without knowing the encryption key. Encryption usually scrambles the original message using a key, called encryption key, that the involved parties agree on. The process of extracting the original message from an encrypted one is called Decryption. Encryption is a process of encoding messages such that it can only be read and understood by the intended parties.
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