aes-256-cfb

README

aes-256-cfb example

AES-256 CFB (Cipher FeedBack) mode is almost identical to CBC mode but performed in reverse.

I have the following AES-256 mode examples,

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

GitHub Webpage

RUN

run aes-cfb.go

You output should be,

Original Text:           This is AES-256 CFB!!

The 32-byte Key:         myverystrongpasswordo32bitlength
The Nonce:               3f267a60bf96b424fa144da8fc4869d4

Encrypted Text:          6a2544cec434601d000afd43d7a1d9edd18f68320a
Decrypted Text:          This is AES-256 CFB!!

HOW IT WORKS

• Makes a block cipher into a self-synchronizing stream cipher
• CFB decryption is almost identical to CBC encryption performed in reverse
• The IV value should be equal to AES block size
• A different nonce is needed for every message
• Encryption but not message integrity

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

Encryption,

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

// GET CFB ENCRYPTER
cfb := cipher.NewCFBEncrypter(block, nonce)

// ENCRYPT DATA
cfb.XORKeyStream(cipherTextByte, plaintextByte)

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

Decryption,

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

// GET CFB DECRYPTER
cfb := cipher.NewCFBDecrypter(block, nonce)

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

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

This illustration may help,