evalphobia/hierogolyph

package chacha20poly1305

import (
    "crypto/rand"
    "fmt"

    "golang.org/x/crypto/chacha20poly1305"
)

const (
    KeySize    = chacha20poly1305.KeySize
    nonceSizeX = chacha20poly1305.NonceSizeX
)

// Encrypt encrypts plainText using XChaCha20-Poly1305.
func Encrypt(plainText string, key []byte) ([]byte, error) {
    // use first 32byte if the key length is longer than 32byte.
    if len(key) > KeySize {
        key = key[0:KeySize]
    }

    aead, err := chacha20poly1305.NewX(key)
    if err != nil {
        return nil, err
    }

    nonce := make([]byte, nonceSizeX)
    if _, err := rand.Read(nonce); err != nil {
        return nil, err
    }

    cipherText := aead.Seal(nil, nonce, []byte(plainText), nil)
    cipherText = append(nonce, cipherText...)
    return cipherText, nil
}

// Decrypt decrypts cipherText using XChaCha20-Poly1305.
func Decrypt(cipherText, key []byte) (string, error) {
    // use first 32byte if the key length is longer than 32byte.
    if len(key) > KeySize {
        key = key[0:KeySize]
    }

    aead, err := chacha20poly1305.NewX(key)
    if err != nil {
        return "", err
    }

    if len(cipherText) < nonceSizeX {
        return "", fmt.Errorf("cipherText is too short: textsize=[%d], noncesize=[%d]", len(cipherText), nonceSizeX)
    }

    nonce := cipherText[:nonceSizeX]
    plainByte, err := aead.Open(nil, nonce, cipherText[nonceSizeX:], nil)
    if err != nil {
        return "", err
    }

    return string(plainByte), nil
}