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Legacy encrypt (current aries RFC 19), compatible with ACA-Py
Closes #139 Signed-off-by: Filip Burlacu <[email protected]>
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Filip Burlacu
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Sep 19, 2019
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,224 @@ | ||
| /* | ||
| Copyright SecureKey Technologies Inc. All Rights Reserved. | ||
| SPDX-License-Identifier: Apache-2.0 | ||
| */ | ||
|
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| package authcrypt | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "crypto/rand" | ||
| "crypto/sha512" | ||
| "encoding/json" | ||
| "errors" | ||
| "fmt" | ||
|
|
||
| "github.com/agl/ed25519/extra25519" | ||
| "golang.org/x/crypto/blake2b" | ||
| chacha "golang.org/x/crypto/chacha20poly1305" | ||
| "golang.org/x/crypto/ed25519" | ||
| "golang.org/x/crypto/nacl/box" | ||
| ) | ||
|
|
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| type privateEd25519 [ed25519.PrivateKeySize]byte | ||
| type publicEd25519 [ed25519.PublicKeySize]byte | ||
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| type keyPairEd25519 struct { | ||
| priv *privateEd25519 | ||
| pub *publicEd25519 | ||
| } | ||
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| // CurveKeySize is the size of public and private Curve25519 keys in bytes | ||
| const CurveKeySize int = 32 | ||
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| type privateCurve25519 [CurveKeySize]byte | ||
| type publicCurve25519 [CurveKeySize]byte | ||
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| type keyPairCurve25519 struct { | ||
| priv *privateCurve25519 | ||
| pub *publicCurve25519 | ||
| } | ||
|
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| // contentEncryption represents a content encryption algorithm. | ||
| type contentEncryption string | ||
|
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| // C20P Chacha20Poly1035 algorithm | ||
| const C20P = contentEncryption("C20P") // Chacha20 encryption + Poly1035 authenticator cipher (96 bits nonce) | ||
|
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| // XC20P XChacha20Poly1035 algorithm | ||
| const XC20P = contentEncryption("XC20P") // XChacha20 encryption + Poly1035 authenticator cipher (192 bits nonce) | ||
|
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| // Crypter represents an Authcrypt Encrypter (Decrypter) that outputs/reads legacy Aries envelopes | ||
| type Crypter struct { | ||
| sender keyPairEd25519 | ||
| recipients []*publicEd25519 | ||
| alg contentEncryption | ||
| nonceSize int | ||
| } | ||
|
|
||
| // New will create a Crypter that encrypts messages using the legacy Aries format | ||
| // Note: legacy crypter does not support XChacha20Poly1035 (XC20P), only Chacha20Poly1035 (C20P) | ||
| func New(sender keyPairEd25519, recipients []*publicEd25519, alg contentEncryption) (*Crypter, error) { | ||
| var nonceSize int | ||
| switch alg { | ||
| case C20P: | ||
| nonceSize = chacha.NonceSize | ||
| default: | ||
| return nil, fmt.Errorf("encryption algorithm '%s' not supported", alg) | ||
| } | ||
|
|
||
| if len(recipients) == 0 { | ||
| return nil, errors.New("empty recipients keys, must have at least one recipient") | ||
| } | ||
| var recipientsKey []*publicEd25519 | ||
| recipientsKey = append(recipientsKey, recipients...) | ||
|
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| c := &Crypter{ | ||
| sender: sender, | ||
| recipients: recipientsKey, | ||
| alg: alg, | ||
| nonceSize: nonceSize, | ||
| } | ||
|
|
||
| if !isKeyPairValid(sender) { | ||
| return nil, fmt.Errorf( | ||
| "sender keyPair not supported, it must have a %d byte private key and %d byte public key", | ||
| ed25519.PrivateKeySize, | ||
| ed25519.PublicKeySize) | ||
| } | ||
|
|
||
| return c, nil | ||
| } | ||
|
|
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| func isKeyPairValid(kp keyPairEd25519) bool { | ||
| if kp.priv == nil || kp.pub == nil { | ||
| return false | ||
| } | ||
|
|
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| return true | ||
| } | ||
|
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| // Envelope is the full payload envelope for the JSON message | ||
| type Envelope struct { | ||
| Protected string `json:"protected,omitempty"` | ||
| IV string `json:"iv,omitempty"` | ||
| CipherText string `json:"ciphertext,omitempty"` | ||
| Tag string `json:"tag,omitempty"` | ||
| } | ||
|
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| // Protected is the protected header of the JSON envelope | ||
| type Protected struct { | ||
| Enc string `json:"enc,omitempty"` | ||
| Typ string `json:"typ,omitempty"` | ||
| Alg string `json:"alg,omitempty"` | ||
| Recipients []Recipient `json:"recipients,omitempty"` | ||
| } | ||
|
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| // Recipient holds the data for a recipient in the envelope header | ||
| type Recipient struct { | ||
| EncryptedKey string `json:"encrypted_key,omitempty"` | ||
| Header RecipientHeader `json:"header,omitempty"` | ||
| } | ||
|
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| // RecipientHeader holds the header data for a recipient | ||
| type RecipientHeader struct { | ||
| KID string `json:"kid,omitempty"` | ||
| Sender string `json:"sender,omitempty"` | ||
| IV string `json:"iv,omitempty"` | ||
| } | ||
|
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| // publicEd25519toCurve25519 takes an Ed25519 public key and provides the corresponding Curve25519 public key | ||
| // This function wraps PublicKeyToCurve25519 from Adam Langley's ed25519 repo: github.com/agl/ed25519 | ||
| func publicEd25519toCurve25519(pub *publicEd25519) (*publicCurve25519, error) { | ||
| pkOut := new([CurveKeySize]byte) | ||
| success := extra25519.PublicKeyToCurve25519(pkOut, (*[CurveKeySize]byte)(pub)) | ||
| if !success { | ||
| return nil, errors.New("failed to convert public key") | ||
| } | ||
| return (*publicCurve25519)(pkOut), nil | ||
| } | ||
|
|
||
| // TODO: consider wrapping agl's secret key conversion instead of reimplementing | ||
|
|
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| // secretEd25519toCurve25519 converts a secret key from Ed25519 to curve25519 format | ||
| // Made with reference to https://github.com/agl/ed25519/blob/master/extra25519/extra25519.go and | ||
| // https://github.com/jedisct1/libsodium/blob/master/src/libsodium/crypto_sign/ed25519/ref10/keypair.c#L70 | ||
| func secretEd25519toCurve25519(priv *privateEd25519) (*privateCurve25519, error) { | ||
| hasher := sha512.New() | ||
| _, err := hasher.Write(priv[:32]) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| hash := hasher.Sum(nil) | ||
|
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| hash[0] &= 248 // clr lower 3 bits | ||
| hash[31] &= 127 // clr upper 1 bit | ||
| hash[31] |= 64 // set 6th bit | ||
|
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| out := new([CurveKeySize]byte) | ||
| copy(out[:], hash) | ||
| return (*privateCurve25519)(out), nil | ||
| } | ||
|
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| func makeNonce(pub1, pub2 []byte) ([]byte, error) { | ||
| var nonce [24]byte | ||
| // generate an equivalent nonce to libsodium's (see link above) | ||
| nonceWriter, err := blake2b.New(24, nil) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| _, err = nonceWriter.Write(pub1) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| _, err = nonceWriter.Write(pub2) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| nonceOut := nonceWriter.Sum(nil) | ||
| copy(nonce[:], nonceOut) | ||
|
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| return nonce[:], nil | ||
| } | ||
|
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| // TODO dupe of jwe/authcrypt encryptOID, refactor out | ||
|
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| // sodiumBoxSeal will encrypt a msg (in the case of this package, it will be | ||
| // an ephemeral key concatenated to the sender's public key) using the | ||
| // recipient's pubKey, this is equivalent to libsodium's C function: crypto_box_seal() | ||
| // https://libsodium.gitbook.io/doc/public-key_cryptography/sealed_boxes#usage | ||
| func sodiumBoxSeal(msg []byte, recPub *publicCurve25519) ([]byte, error) { | ||
| var nonce [24]byte | ||
| // generate ephemeral curve25519 asymmetric keys | ||
| epk, esk, err := box.GenerateKey(rand.Reader) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| // generate an equivalent nonce to libsodium's (see link above) | ||
| nonceSlice, err := makeNonce(epk[:], recPub[:]) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| copy(nonce[:], nonceSlice) | ||
|
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| var out = make([]byte, len(epk)) | ||
| copy(out, epk[:]) | ||
|
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| // now seal the msg with the ephemeral key, nonce and recPub (which is recipient's publicKey) | ||
| ret := box.Seal(out, msg, &nonce, (*[32]byte)(recPub), esk) | ||
|
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| return ret, nil | ||
| } | ||
|
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| func prettyPrint(msg []byte) (string, error) { | ||
| var prettyJSON bytes.Buffer | ||
| err := json.Indent(&prettyJSON, msg, "", "\t") | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
|
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| return prettyJSON.String(), nil | ||
| } |
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