XOR encryption

XOR encryption is a trivially simple symmetric cipher which is used in many applications where security is not a defined requirement.

The XOR Operator

XOR, also know as Exclusive OR, is a bitwise operator from binary mathematics.

The six bitwise operators, as defined in the C programming language, are:

Operation	Symbol
AND	&
Inclusive OR	|
Exclusive OR (XOR)	^
Right Shift	>>
Left Shift	<<
Complement	~

The XOR operator returns a 1 when the value of either the first bit or the second bit is a 1.

The XOR operator returns a 0 when neither or both of the bits is 1.

This is best illustrated in the following chart:

First Bit	Second Bit	Result
0	0	0
0	1	1
1	0	1
1	1	0

The XOR operator is used to "flip" bits (zeroes and ones) in a piece of plaintext to create a ciphertext.

Converting Plaintext to Ciphertext with XOR Encryption

The plaintext we will start with is the term "FAQ".

• ASCII representation of the plaintext: FAQ
• Hexadecimal representation of the plaintext: 70 65 81
• Binary representation of the plaintext: 01110000 01100101 1000000

We will XOR the first character of this plaintext into ciphertext using a "V" as the key:

• ASCII representation of the key: V
• Hexadecimal representation of the key: 86
• Binary representation of the key: 10000110

Plaintext 'F'	Key 'V'	Ciphertext
0	1	1
1	0	1
1	0	1
1	0	1
0	0	0
0	1	1
0	0	0
0	1	1

Converting Ciphertext to Plaintext with XOR Encryption

XOR encryption is a symmetric algorithm. This means that we can use the encryption key as the decryption key.

Let's decrypt our ciphertext to recreate our original plaintext.

Ciphertext	Key 'V'	Plaintext
1	1	0
1	0	1
1	0	1
1	0	1
0	0	0
1	1	0
0	0	0
1	1	0

Do the math yourself with the other two characters of plaintext to prove this to yourself.

Many encryption algorithms utilize the XOR operator as part of their operations.

Understanding XOR and the other binary operators is a necessary step on the path to becoming a cryptologist.

XOR Security

XOR encryption is trivially simple to implement and equally trivial to break.

XOR encryption should not be utilized for any data which you would want to protect.