106 lines
3.0 KiB
Go
106 lines
3.0 KiB
Go
package crypto
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"crypto/sha256"
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"encoding/hex"
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"errors"
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"fmt"
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"io"
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"golang.org/x/crypto/pbkdf2"
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)
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const (
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// PBKDF2Iterations defines the mandatory 100,000 rounds of PBKDF2 key derivation.
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PBKDF2Iterations = 100000
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// KeyLength is 32 bytes for AES-256.
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KeyLength = 32
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// SaltLength is 16 bytes minimum.
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SaltLength = 16
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)
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var (
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ErrCiphertextTooShort = errors.New("ciphertext too short")
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ErrDecryptionFailed = errors.New("decryption failed or corrupted data")
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)
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// DeriveKey derives a 32-byte AES-256 key from a passphrase and salt using PBKDF2 with 100,000 iterations.
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func DeriveKey(passphrase string, salt []byte) []byte {
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return pbkdf2.Key([]byte(passphrase), salt, PBKDF2Iterations, KeyLength, sha256.New)
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}
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// GenerateSalt creates a cryptographically secure random salt of the specified length.
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func GenerateSalt(length int) ([]byte, error) {
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if length < SaltLength {
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length = SaltLength
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}
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salt := make([]byte, length)
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if _, err := io.ReadFull(rand.Reader, salt); err != nil {
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return nil, fmt.Errorf("failed to generate random salt: %w", err)
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}
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return salt, nil
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}
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// GenerateToken generates a cryptographically random 32-byte hex token.
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func GenerateToken() (string, error) {
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b := make([]byte, 32)
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if _, err := io.ReadFull(rand.Reader, b); err != nil {
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return "", fmt.Errorf("failed to generate token: %w", err)
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}
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return hex.EncodeToString(b), nil
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}
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// Encrypt encrypts plaintext using AES-256-GCM with a random 12-byte nonce.
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// The output format is: [nonce (12 bytes)] + [ciphertext + 16-byte auth tag].
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func Encrypt(key, plaintext []byte) ([]byte, error) {
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if len(key) != KeyLength {
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return nil, fmt.Errorf("invalid key length: must be %d bytes", KeyLength)
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, fmt.Errorf("failed to create cipher block: %w", err)
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}
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gcm, err := cipher.NewGCM(block)
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if err != nil {
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return nil, fmt.Errorf("failed to create GCM: %w", err)
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}
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nonce := make([]byte, gcm.NonceSize())
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if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
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return nil, fmt.Errorf("failed to generate nonce: %w", err)
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}
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ciphertext := gcm.Seal(nonce, nonce, plaintext, nil)
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return ciphertext, nil
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}
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// Decrypt decrypts AES-256-GCM ciphertext created by Encrypt.
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func Decrypt(key, ciphertext []byte) ([]byte, error) {
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if len(key) != KeyLength {
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return nil, fmt.Errorf("invalid key length: must be %d bytes", KeyLength)
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, fmt.Errorf("failed to create cipher block: %w", err)
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}
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gcm, err := cipher.NewGCM(block)
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if err != nil {
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return nil, fmt.Errorf("failed to create GCM: %w", err)
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}
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nonceSize := gcm.NonceSize()
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if len(ciphertext) < nonceSize {
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return nil, ErrCiphertextTooShort
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}
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nonce, actualCiphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]
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plaintext, err := gcm.Open(nil, nonce, actualCiphertext, nil)
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if err != nil {
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return nil, ErrDecryptionFailed
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}
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return plaintext, nil
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}
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