| 1 | package docs |
| 2 | |
| 3 | import ( |
| 4 | "crypto/aes" |
| 5 | "crypto/cipher" |
| 6 | "crypto/rand" |
| 7 | "crypto/sha256" |
| 8 | "encoding/base64" |
| 9 | "encoding/binary" |
| 10 | "encoding/hex" |
| 11 | "errors" |
| 12 | "strings" |
| 13 | |
| 14 | "github.com/google/uuid" |
| 15 | ) |
| 16 | |
| 17 | const contentEncoding = 1 |
| 18 | const contentUpdateKind byte = 1 |
| 19 | const contentSnapshotKind byte = 2 |
| 20 | const contentKeyCheckKind byte = 3 |
| 21 | |
| 22 | var developmentContentKey = sha256.Sum256([]byte("docs-development-content-key-not-a-secret")) |
| 23 | var errContentKey = errors.New("docs: invalid content key") |
| 24 | var errContentAuthentication = errors.New("docs: content authentication failed") |
| 25 | var errContentEncoding = errors.New("docs: unsupported content encoding") |
| 26 | |
| 27 | type contentCipher struct { |
| 28 | aead cipher.AEAD |
| 29 | fingerprint string |
| 30 | } |
| 31 | |
| 32 | func newContentCipher(encoded, env string) (*contentCipher, error) { |
| 33 | encoded = strings.TrimSpace(encoded) |
| 34 | var key []byte |
| 35 | if encoded == "" && env == "development" { |
| 36 | key = developmentContentKey[:] |
| 37 | } else { |
| 38 | var err error |
| 39 | key, err = base64.StdEncoding.Strict().DecodeString(encoded) |
| 40 | if err != nil || len(key) != 32 { |
| 41 | return nil, errContentKey |
| 42 | } |
| 43 | } |
| 44 | fingerprint := sha256.Sum256(key) |
| 45 | devFingerprint := sha256.Sum256(developmentContentKey[:]) |
| 46 | if env != "development" && fingerprint == devFingerprint { |
| 47 | return nil, errContentKey |
| 48 | } |
| 49 | block, err := aes.NewCipher(key) |
| 50 | if err != nil { |
| 51 | return nil, errContentKey |
| 52 | } |
| 53 | aead, err := cipher.NewGCM(block) |
| 54 | if err != nil { |
| 55 | return nil, err |
| 56 | } |
| 57 | return &contentCipher{aead: aead, fingerprint: hex.EncodeToString(fingerprint[:])}, nil |
| 58 | } |
| 59 | |
| 60 | func contentAAD(kind byte, guid string, seq int64, abi uint32) ([]byte, error) { |
| 61 | id, err := uuid.Parse(guid) |
| 62 | if err != nil || seq < 0 { |
| 63 | return nil, errContentAuthentication |
| 64 | } |
| 65 | aad := append([]byte("oficina/docs/content/v1"), kind) |
| 66 | aad = append(aad, id[:]...) |
| 67 | aad = binary.BigEndian.AppendUint64(aad, uint64(seq)) |
| 68 | aad = binary.BigEndian.AppendUint32(aad, abi) |
| 69 | return aad, nil |
| 70 | } |
| 71 | |
| 72 | func (c *contentCipher) seal(kind byte, guid string, seq int64, abi uint32, plaintext []byte) ([]byte, error) { |
| 73 | aad, err := contentAAD(kind, guid, seq, abi) |
| 74 | if err != nil { |
| 75 | return nil, err |
| 76 | } |
| 77 | nonce := make([]byte, c.aead.NonceSize()) |
| 78 | if _, err := rand.Read(nonce); err != nil { |
| 79 | return nil, err |
| 80 | } |
| 81 | return c.aead.Seal(nonce, nonce, plaintext, aad), nil |
| 82 | } |
| 83 | |
| 84 | func (c *contentCipher) open(kind byte, guid string, seq int64, abi uint32, sealed []byte) ([]byte, error) { |
| 85 | aad, err := contentAAD(kind, guid, seq, abi) |
| 86 | if err != nil || len(sealed) < c.aead.NonceSize()+c.aead.Overhead() { |
| 87 | return nil, errContentAuthentication |
| 88 | } |
| 89 | n := c.aead.NonceSize() |
| 90 | plaintext, err := c.aead.Open(nil, sealed[:n], sealed[n:], aad) |
| 91 | if err != nil { |
| 92 | return nil, errContentAuthentication |
| 93 | } |
| 94 | return plaintext, nil |
| 95 | } |
| 96 | |
amadan