| 1 | package maintenance |
| 2 | |
| 3 | import ( |
| 4 | "crypto/aes" |
| 5 | "crypto/cipher" |
| 6 | "crypto/ecdh" |
| 7 | "crypto/rand" |
| 8 | "crypto/sha256" |
| 9 | "encoding/base64" |
| 10 | "encoding/binary" |
| 11 | "encoding/hex" |
| 12 | "errors" |
| 13 | "io" |
| 14 | |
| 15 | "golang.org/x/crypto/hkdf" |
| 16 | ) |
| 17 | |
| 18 | const ( |
| 19 | EnvelopeVersion uint32 = 1 |
| 20 | // MaxEnvelopePlaintext bounds the crypto allocation. Request/result parsers |
| 21 | // impose their smaller operation-specific limits before execution. |
| 22 | MaxEnvelopePlaintext = 1 << 20 |
| 23 | envelopePrefix = "CME1" |
| 24 | ephemeralBytes = 65 |
| 25 | nonceBytes = 12 |
| 26 | tagBytes = 16 |
| 27 | envelopeInfo = "carlos-maintenance-v1" |
| 28 | ) |
| 29 | |
| 30 | type Direction string |
| 31 | |
| 32 | const ( |
| 33 | DirectionInput Direction = "input" |
| 34 | DirectionResult Direction = "result" |
| 35 | DirectionEnvironment Direction = "environment" |
| 36 | ) |
| 37 | |
| 38 | var ErrEnvelope = errors.New("maintenance: invalid private envelope") |
| 39 | |
| 40 | // Binding authenticates identifiers already validated by the request handler. |
| 41 | // It does not establish ownership or authorize an operation. |
| 42 | type Binding struct { |
| 43 | Version uint32 |
| 44 | Direction Direction |
| 45 | Account string |
| 46 | App string |
| 47 | Host string |
| 48 | RequestID string |
| 49 | AttemptID string |
| 50 | Recipient string |
| 51 | } |
| 52 | |
| 53 | // RecipientFingerprint names the P-256 key that can open the envelope. |
| 54 | func RecipientFingerprint(pub *ecdh.PublicKey) (string, error) { |
| 55 | if pub == nil || pub.Curve() != ecdh.P256() { |
| 56 | return "", ErrEnvelope |
| 57 | } |
| 58 | sum := sha256.Sum256(pub.Bytes()) |
| 59 | return hex.EncodeToString(sum[:]), nil |
| 60 | } |
| 61 | |
| 62 | func appendField(dst []byte, field []byte) []byte { |
| 63 | dst = binary.BigEndian.AppendUint32(dst, uint32(len(field))) |
| 64 | return append(dst, field...) |
| 65 | } |
| 66 | func bindingAAD(b Binding, pub *ecdh.PublicKey) ([]byte, error) { |
| 67 | fingerprint, err := RecipientFingerprint(pub) |
| 68 | if err != nil || b.Version != EnvelopeVersion || b.Recipient != fingerprint { |
| 69 | return nil, ErrEnvelope |
| 70 | } |
| 71 | if b.Direction != DirectionInput && b.Direction != DirectionResult && b.Direction != DirectionEnvironment { |
| 72 | return nil, ErrEnvelope |
| 73 | } |
| 74 | fields := []struct { |
| 75 | s string |
| 76 | max int |
| 77 | }{{b.Account, 64}, {b.App, 64}, {b.Host, 253}, {b.RequestID, 64}, {b.AttemptID, 64}} |
| 78 | for _, f := range fields { |
| 79 | if len(f.s) == 0 || len(f.s) > f.max { |
| 80 | return nil, ErrEnvelope |
| 81 | } |
| 82 | for i := range len(f.s) { |
| 83 | if f.s[i] < 0x21 || f.s[i] > 0x7e { |
| 84 | return nil, ErrEnvelope |
| 85 | } |
| 86 | } |
| 87 | } |
| 88 | aad := appendField(nil, []byte(envelopePrefix)) |
| 89 | aad = appendField(aad, binary.BigEndian.AppendUint32(nil, b.Version)) |
| 90 | aad = appendField(aad, []byte(b.Direction)) |
| 91 | for _, f := range fields { |
| 92 | aad = appendField(aad, []byte(f.s)) |
| 93 | } |
| 94 | return appendField(aad, []byte(b.Recipient)), nil |
| 95 | } |
| 96 | func envelopeGCM(shared []byte) (cipher.AEAD, error) { |
| 97 | key := make([]byte, 32) |
| 98 | if _, err := io.ReadFull(hkdf.New(sha256.New, shared, nil, []byte(envelopeInfo)), key); err != nil { |
| 99 | return nil, ErrEnvelope |
| 100 | } |
| 101 | block, err := aes.NewCipher(key) |
| 102 | clear(key) |
| 103 | if err != nil { |
| 104 | return nil, ErrEnvelope |
| 105 | } |
| 106 | gcm, err := cipher.NewGCM(block) |
| 107 | if err != nil { |
| 108 | return nil, ErrEnvelope |
| 109 | } |
| 110 | return gcm, nil |
| 111 | } |
| 112 | |
| 113 | // Seal encrypts private input, output or an environment snapshot for one |
| 114 | // recipient and one immutable operation binding. |
| 115 | func Seal(pub *ecdh.PublicKey, b Binding, plaintext []byte) (string, error) { |
| 116 | if len(plaintext) > MaxEnvelopePlaintext { |
| 117 | return "", ErrEnvelope |
| 118 | } |
| 119 | if _, err := bindingAAD(b, pub); err != nil { |
| 120 | return "", ErrEnvelope |
| 121 | } |
| 122 | eph, err := ecdh.P256().GenerateKey(rand.Reader) |
| 123 | if err != nil { |
| 124 | return "", ErrEnvelope |
| 125 | } |
| 126 | nonce := make([]byte, nonceBytes) |
| 127 | if _, err := io.ReadFull(rand.Reader, nonce); err != nil { |
| 128 | return "", ErrEnvelope |
| 129 | } |
| 130 | return sealWith(eph, nonce, pub, b, plaintext) |
| 131 | } |
| 132 | |
| 133 | // sealWith permits deterministic vectors without replacing production entropy. |
| 134 | func sealWith(eph *ecdh.PrivateKey, nonce []byte, pub *ecdh.PublicKey, b Binding, plaintext []byte) (string, error) { |
| 135 | if eph == nil || eph.Curve() != ecdh.P256() || len(nonce) != nonceBytes || len(plaintext) > MaxEnvelopePlaintext { |
| 136 | return "", ErrEnvelope |
| 137 | } |
| 138 | aad, err := bindingAAD(b, pub) |
| 139 | if err != nil { |
| 140 | return "", ErrEnvelope |
| 141 | } |
| 142 | shared, err := eph.ECDH(pub) |
| 143 | if err != nil { |
| 144 | return "", ErrEnvelope |
| 145 | } |
| 146 | defer clear(shared) |
| 147 | gcm, err := envelopeGCM(shared) |
| 148 | if err != nil { |
| 149 | return "", ErrEnvelope |
| 150 | } |
| 151 | raw := make([]byte, 0, len(envelopePrefix)+ephemeralBytes+nonceBytes+len(plaintext)+tagBytes) |
| 152 | raw = append(raw, []byte(envelopePrefix)...) |
| 153 | raw = append(raw, eph.PublicKey().Bytes()...) |
| 154 | raw = append(raw, nonce...) |
| 155 | raw = gcm.Seal(raw, nonce, plaintext, aad) |
| 156 | return base64.StdEncoding.EncodeToString(raw), nil |
| 157 | } |
| 158 | |
| 159 | // Open refuses changed bindings and noncanonical or oversized envelopes before |
| 160 | // returning plaintext. No error includes caller input or decrypted material. |
| 161 | func Open(priv *ecdh.PrivateKey, b Binding, envelope string) ([]byte, error) { |
| 162 | const overhead = len(envelopePrefix) + ephemeralBytes + nonceBytes + tagBytes |
| 163 | if priv == nil || priv.Curve() != ecdh.P256() || len(envelope) > base64.StdEncoding.EncodedLen(overhead+MaxEnvelopePlaintext) { |
| 164 | return nil, ErrEnvelope |
| 165 | } |
| 166 | aad, err := bindingAAD(b, priv.PublicKey()) |
| 167 | if err != nil { |
| 168 | return nil, ErrEnvelope |
| 169 | } |
| 170 | raw, err := base64.StdEncoding.Strict().DecodeString(envelope) |
| 171 | if err != nil || len(raw) < overhead || len(raw) > overhead+MaxEnvelopePlaintext || base64.StdEncoding.EncodeToString(raw) != envelope { |
| 172 | return nil, ErrEnvelope |
| 173 | } |
| 174 | if string(raw[:len(envelopePrefix)]) != envelopePrefix { |
| 175 | return nil, ErrEnvelope |
| 176 | } |
| 177 | pointEnd := len(envelopePrefix) + ephemeralBytes |
| 178 | eph, err := ecdh.P256().NewPublicKey(raw[len(envelopePrefix):pointEnd]) |
| 179 | if err != nil { |
| 180 | return nil, ErrEnvelope |
| 181 | } |
| 182 | shared, err := priv.ECDH(eph) |
| 183 | if err != nil { |
| 184 | return nil, ErrEnvelope |
| 185 | } |
| 186 | defer clear(shared) |
| 187 | gcm, err := envelopeGCM(shared) |
| 188 | if err != nil { |
| 189 | return nil, ErrEnvelope |
| 190 | } |
| 191 | plaintext, err := gcm.Open(nil, raw[pointEnd:pointEnd+nonceBytes], raw[pointEnd+nonceBytes:], aad) |
| 192 | if err != nil { |
| 193 | return nil, ErrEnvelope |
| 194 | } |
| 195 | return plaintext, nil |
| 196 | } |
| 197 | |
amadan