aes-256-gcm

README

aes-256-gcm example

AES-256 GCM (Galois/Counter Mode) mode is a block cipher counter mode with authentication.

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 (You are here) (I like this one)
• aes-256-ofb Output FeedBack Mode

GitHub Webpage

RUN

run aes-gcm.go

Your output should be similar,

Original Text:           This is an example of AES-256 GCM.

The 32-byte Key:         myverystrongpasswordo32bitlength
Additional Data:         Jeff's additional data for authorization
The Nonce:               f796b0e6a7fabdf9cb6e6d4e

Encrypted Text:          f796b0e6a7fabdf9cb6e6d4ed4109c9538107d3b9a28ecefde2b69608798209ca9ae3932e7ddc1c1884d2bb7d3aed3d85ed56a9f60389503b9b7c08e8121
Decrypted Text:          This is an example of AES-256 GCM.

Note how you an see the nonce at the beginning of the encrypted text. Its because I put it there so I can extract it during decrypt.

HOW IT WORKS

• A Counter mode effectively turns a block cipher into a stream cipher,
• GCM uses an IV (Initialization Vector) or Nonce
• I also used some Additional Data for authentication

Encryption using your gcm block,

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

// GET GCM INSTANCE THAT USES THE AES CIPHER
gcm, err := cipher.NewGCM(block)

// ENCRYPT DATA
cipherTextByte := gcm.Seal(nonce, nonce, plaintextByte, additionalDataByte)

Decryption using your gcm block,

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

// GET GCM BLOCK
gcm, err := cipher.NewGCM(block)

// DECRYPT DATA
plainTextByte, err := gcm.Open(nil, nonce, cipherTextByte, additionalDataByte)

This illustration may help,