mirror of
https://github.com/sartoopjj/thefeed.git
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Sarto
109 lines
3.3 KiB
Go
109 lines
3.3 KiB
Go
package protocol
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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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"fmt"
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"io"
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"golang.org/x/crypto/hkdf"
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)
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const (
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KeySize = 32 // AES-256
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NonceSize = 12 // GCM nonce
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)
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// DeriveKeys derives separate query and response AES-256 keys from a passphrase using HKDF.
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func DeriveKeys(passphrase string) (queryKey, responseKey [KeySize]byte, err error) {
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master := sha256.Sum256([]byte(passphrase))
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qr := hkdf.New(sha256.New, master[:], nil, []byte("thefeed-query"))
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if _, err = io.ReadFull(qr, queryKey[:]); err != nil {
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return
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}
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rr := hkdf.New(sha256.New, master[:], nil, []byte("thefeed-response"))
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_, err = io.ReadFull(rr, responseKey[:])
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return
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}
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func newGCM(key [KeySize]byte) (cipher.AEAD, error) {
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block, err := aes.NewCipher(key[:])
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if err != nil {
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return nil, err
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}
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return cipher.NewGCM(block)
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}
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// Encrypt encrypts plaintext using AES-256-GCM. Returns nonce+ciphertext+tag.
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func Encrypt(key [KeySize]byte, plaintext []byte) ([]byte, error) {
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gcm, err := newGCM(key)
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if err != nil {
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return nil, 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("generate nonce: %w", err)
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}
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return gcm.Seal(nonce, nonce, plaintext, nil), nil
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}
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// Decrypt decrypts AES-256-GCM ciphertext (nonce+ciphertext+tag).
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func Decrypt(key [KeySize]byte, ciphertext []byte) ([]byte, error) {
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gcm, err := newGCM(key)
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if err != nil {
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return nil, err
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}
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if len(ciphertext) < gcm.NonceSize()+gcm.Overhead() {
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return nil, fmt.Errorf("ciphertext too short: %d bytes", len(ciphertext))
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}
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nonce := ciphertext[:gcm.NonceSize()]
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return gcm.Open(nil, nonce, ciphertext[gcm.NonceSize():], nil)
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}
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// encryptQueryBlock encrypts an 8-byte query payload using a direct AES-256 block cipher.
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// The payload is expanded to one AES block (16 bytes) with 8 trailing zero bytes before
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// encryption. No nonce or auth tag needed: the 4 random bytes in the payload guarantee
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// unique ciphertext per query. Result is always 16 bytes.
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func encryptQueryBlock(key [KeySize]byte, payload []byte) ([]byte, error) {
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if len(payload) != QueryPayloadSize {
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return nil, fmt.Errorf("encryptQueryBlock: payload must be %d bytes, got %d", QueryPayloadSize, len(payload))
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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, err
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}
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var buf [aes.BlockSize]byte
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copy(buf[:QueryPayloadSize], payload) // bytes 8-15 stay zero
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block.Encrypt(buf[:], buf[:])
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return buf[:], nil
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}
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// decryptQueryBlock decrypts a query ciphertext produced by encryptQueryBlock.
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// Accepts ciphertext with optional random suffix bytes (≥ BlockSize); only the
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// first BlockSize bytes are used. Verifies the last 8 bytes of plaintext are zero.
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func decryptQueryBlock(key [KeySize]byte, ciphertext []byte) ([]byte, error) {
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if len(ciphertext) < aes.BlockSize {
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return nil, fmt.Errorf("decryptQueryBlock: need at least %d bytes, got %d", aes.BlockSize, len(ciphertext))
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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, err
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}
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var buf [aes.BlockSize]byte
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block.Decrypt(buf[:], ciphertext[:aes.BlockSize]) // ignore suffix
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for i := QueryPayloadSize; i < aes.BlockSize; i++ {
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if buf[i] != 0 {
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return nil, fmt.Errorf("decryptQueryBlock: integrity check failed (wrong key?)")
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}
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}
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return buf[:QueryPayloadSize], nil
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}
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