aes-256-ofb

README

aes-256-ofb example

AES-256 OFB (Output FeedBack) mode which makes a block cipher into a synchronous stream cipher. It generates keystream blocks, which are XORed with the plaintext blocks to get the cipherText.

I have the following AES-256 mode examples,

• aes-256 No Mode
• aes-256-cbc Cipher Block Chaining
• aes-256-cfb Cipher FeedBack Mode
• aes-256-ctr Counter Mode
• aes-256-gcm Galois/Counter Mode (I like this one)
• aes-256-ofb Output FeedBack Mode (You are here)

GitHub Webpage

RUN

run aes-ofb.go

You output should be,

Original Text:           This is AES-256 OFB (32 Bytes)!!

The 32-byte Key:         myverystrongpasswordo32bitlength
The Nonce:               0781d57b73411cac0a355394c7de214c

Encrypted Text:          f924dec67731adc6ea519e064a50607da1b62acaefb1444a846a93ca200c4919
Decrypted Text:          This is AES-256 OFB (32 Bytes)!!

HOW IT WORKS

• plainText must be multiple of AES block size, you can add padding
• Nonce should be equal to AES block size
• OFB is block ciphers modes, encryption but not message integrity
• Because of the symmetry of the XOR operation, encryption and decryption are exactly the same

For simplicity I did not include the nonce in the cipherText.

Encryption,

// GET CIPHER BLOCK USING KEY
block, err := aes.NewCipher(keyByte)

// GET OFB
ofb := cipher.NewOFB(block, nonce)

// ENCRYPT DATA
ofb.XORKeyStream(cipherTextByte, plainTextByte)

// RETURN HEX
cipherText := hex.EncodeToString(cipherTextByte)

Decryption,

// GET CIPHER BLOCK USING KEY
block, err := aes.NewCipher(keyByte)

// GET OFB
ofb := cipher.NewOFB(block, nonce)

// DECRYPT DATA
ofb.XORKeyStream(plainTextByte, cipherTextByte)

// RETURN STRING
plainText := string(plainTextByte[:])

This illustration may help,