Claus Lohmar
76a4a6950c
- webauthn: the passkey ceremony service (a fake in tests) - totp: the TOTP authenticator; the secret is AEAD-sealed at rest (A9) - sealer: the AEAD TOTP sealer - identities/sessions/credentials: the GUID state machine - flow: the enroll/login screens + the passkey nudge (pre-session double-submit CSRF — A15), rendered inside the shell
73 lines
2 KiB
Go
73 lines
2 KiB
Go
package auth
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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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"fmt"
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)
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// Sealer is the encryption seam for TOTP secrets at rest (A9). The key comes
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// from config later (D-035); this package only defines the mechanism.
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//
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// A Sealer must return ciphertext that never equals — and never contains — the
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// plaintext.
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type Sealer interface {
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Seal(plaintext []byte) ([]byte, error)
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Open(ciphertext []byte) ([]byte, error)
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}
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// KeySize is the AES-256 key length required by AEADSealer.
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const KeySize = 32
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// AEADSealer encrypts with AES-256-GCM. The stored blob is
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//
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// nonce || ciphertext || tag
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//
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// A fresh random nonce is generated on every Seal, so sealing the same secret
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// twice yields different ciphertext.
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type AEADSealer struct {
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aead cipher.AEAD
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}
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// NewAEADSealer builds a Sealer from a 32-byte key.
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func NewAEADSealer(key []byte) (*AEADSealer, error) {
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if len(key) != KeySize {
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return nil, fmt.Errorf("auth: TOTP encryption key must be %d bytes, got %d", KeySize, len(key))
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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("auth: new cipher: %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("auth: new GCM: %w", err)
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}
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return &AEADSealer{aead: gcm}, nil
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}
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// Seal encrypts plaintext.
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func (s *AEADSealer) Seal(plaintext []byte) ([]byte, error) {
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nonce := make([]byte, s.aead.NonceSize())
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if _, err := rand.Read(nonce); err != nil {
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return nil, fmt.Errorf("auth: seal nonce: %w", err)
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}
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// Seal appends to nonce, producing nonce || ciphertext||tag.
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return s.aead.Seal(nonce, nonce, plaintext, nil), nil
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}
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// Open decrypts a blob produced by Seal.
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func (s *AEADSealer) Open(ciphertext []byte) ([]byte, error) {
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ns := s.aead.NonceSize()
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if len(ciphertext) < ns {
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return nil, ErrInvalidCiphertext
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}
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nonce, ct := ciphertext[:ns], ciphertext[ns:]
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plaintext, err := s.aead.Open(nil, nonce, ct, nil)
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if err != nil {
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return nil, fmt.Errorf("%w: %v", ErrInvalidCiphertext, err)
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}
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return plaintext, nil
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}
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var _ Sealer = (*AEADSealer)(nil)
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