chacha20poly1305

Documentation

Overview

Package chacha20poly1305 implements the ChaCha20-Poly1305 AEAD as specified in RFC 7539, and its extended nonce variant XChaCha20-Poly1305.

Index

• Constants
• func New(key []byte) (cipher.AEAD, error)
• func NewX(key []byte) (cipher.AEAD, error)

Examples

• NewX

Constants

const (
	// KeySize is the size of the key used by this AEAD, in bytes.
	KeySize = 32

	// NonceSize is the size of the nonce used with the standard variant of this
	// AEAD, in bytes.
	//
	// Note that this is too short to be safely generated at random if the same
	// key is reused more than 2³² times.
	NonceSize = 12

	// NonceSizeX is the size of the nonce used with the XChaCha20-Poly1305
	// variant of this AEAD, in bytes.
	NonceSizeX = 24
)

Functions

func New

func New(key []byte) (cipher.AEAD, error)

New returns a ChaCha20-Poly1305 AEAD that uses the given 256-bit key.

func NewX

func NewX(key []byte) (cipher.AEAD, error)

NewX returns a XChaCha20-Poly1305 AEAD that uses the given 256-bit key.

XChaCha20-Poly1305 is a ChaCha20-Poly1305 variant that takes a longer nonce, suitable to be generated randomly without risk of collisions. It should be preferred when nonce uniqueness cannot be trivially ensured, or whenever nonces are randomly generated.

Example

aead, err := NewX(key)
if err != nil {
	log.Fatalln("Failed to instantiate XChaCha20-Poly1305:", err)
}

for _, msg := range []string{
	"Attack at dawn.",
	"The eagle has landed.",
	"Gophers, gophers, gophers everywhere!",
} {
	// Encryption.
	nonce := make([]byte, NonceSizeX)
	if _, err := cryptorand.Read(nonce); err != nil {
		panic(err)
	}
	ciphertext := aead.Seal(nil, nonce, []byte(msg), nil)

	// Decryption.
	plaintext, err := aead.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		log.Fatalln("Failed to decrypt or authenticate message:", err)
	}

	fmt.Printf("%s\n", plaintext)
}

Output:

Attack at dawn.
The eagle has landed.
Gophers, gophers, gophers everywhere!