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package internal
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/base64"
"errors"
"fmt"
"io"
"os"
)
func NewKEKFromEnvB64(envVar string) (KEK, error) {
b64 := os.Getenv(envVar)
if b64 == "" {
return nil, fmt.Errorf("%s is not set", envVar)
}
raw, err := base64.StdEncoding.DecodeString(b64)
if err != nil {
return nil, fmt.Errorf("decode %s base64: %w", envVar, err)
}
if !validAESKeyLen(len(raw)) {
return nil, errBadKeyLn
}
return KEK(raw), nil
}
func NewDEK() (DEK, error) {
key := make([]byte, 32) // AES-256
if _, err := io.ReadFull(rand.Reader, key); err != nil {
return nil, fmt.Errorf("random DEK gen: %w", err)
}
return DEK(key), nil
}
func WrapDEK(dek DEK, kek KEK) (WrappedDEK, error) {
edek, err := encryptAEAD([]byte(dek), []byte(kek), aadWrapDEK)
return WrappedDEK(edek), err
}
func UnwrapDEK(edek WrappedDEK, kek KEK) (DEK, error) {
dek, err := decryptAEAD([]byte(edek), []byte(kek), aadWrapDEK)
return DEK(dek), err
}
func EncryptData(plaintext []byte, dek DEK) (Ciphertext, error) {
ct, err := encryptAEAD(plaintext, []byte(dek), aadDataMsg)
return Ciphertext(ct), err
}
func DecryptData(ct Ciphertext, dek DEK) ([]byte, error) {
return decryptAEAD([]byte(ct), []byte(dek), aadDataMsg)
}
// encryptAEAD returns: nonce || ciphertext
func encryptAEAD(plaintext, key, aad []byte) ([]byte, error) {
if !validAESKeyLen(len(key)) {
return nil, errBadKeyLn
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
gcm, err := cipher.NewGCM(block)
if err != nil {
return nil, err
}
nonce := make([]byte, gcm.NonceSize())
if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
return nil, err
}
return gcm.Seal(nonce, nonce, plaintext, aad), nil
}
func decryptAEAD(ciphertext, key, aad []byte) ([]byte, error) {
if !validAESKeyLen(len(key)) {
return nil, errBadKeyLn
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
gcm, err := cipher.NewGCM(block)
if err != nil {
return nil, err
}
ns := gcm.NonceSize()
if len(ciphertext) < ns {
return nil, errors.New("ciphertext too short")
}
nonce := ciphertext[:ns]
body := ciphertext[ns:]
return gcm.Open(nil, nonce, body, aad)
}
func validAESKeyLen(n int) bool {
return n == 16 || n == 24 || n == 32
}
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