mirror of
https://source.quilibrium.com/quilibrium/ceremonyclient.git
synced 2024-11-15 04:35:17 +00:00
116 lines
2.8 KiB
Go
116 lines
2.8 KiB
Go
//
|
||
// Copyright Coinbase, Inc. All Rights Reserved.
|
||
//
|
||
// SPDX-License-Identifier: Apache-2.0
|
||
//
|
||
|
||
package core
|
||
|
||
import (
|
||
"crypto/hmac"
|
||
crand "crypto/rand"
|
||
"crypto/sha256"
|
||
"crypto/subtle"
|
||
"encoding/json"
|
||
"fmt"
|
||
"hash"
|
||
)
|
||
|
||
// Size of random values and hash outputs are determined by our hash function
|
||
const Size = sha256.Size
|
||
|
||
type (
|
||
// Commitment to a given message which can be later revealed.
|
||
// This is sent to and held by a verifier until the corresponding
|
||
// witness is provided.
|
||
Commitment []byte
|
||
|
||
// Witness is sent to and opened by the verifier. This proves that
|
||
// committed message hasn't been altered by later information.
|
||
Witness struct {
|
||
Msg []byte
|
||
r [Size]byte
|
||
}
|
||
|
||
// witnessJSON is used for un/marshaling.
|
||
witnessJSON struct {
|
||
Msg []byte
|
||
R [Size]byte
|
||
}
|
||
)
|
||
|
||
// MarshalJSON encodes Witness in JSON
|
||
func (w Witness) MarshalJSON() ([]byte, error) {
|
||
return json.Marshal(witnessJSON{w.Msg, w.r})
|
||
}
|
||
|
||
// UnmarshalJSON decodes JSON into a Witness struct
|
||
func (w *Witness) UnmarshalJSON(data []byte) error {
|
||
witness := &witnessJSON{}
|
||
err := json.Unmarshal(data, witness)
|
||
if err != nil {
|
||
return err
|
||
}
|
||
w.Msg = witness.Msg
|
||
w.r = witness.R
|
||
return nil
|
||
}
|
||
|
||
// Commit to a given message. Uses SHA256 as the hash function.
|
||
func Commit(msg []byte) (Commitment, *Witness, error) {
|
||
// Initialize our decommitment
|
||
d := Witness{msg, [Size]byte{}}
|
||
|
||
// Generate a random nonce of the required length
|
||
n, err := crand.Read(d.r[:])
|
||
// Ensure no errors retrieving nonce
|
||
if err != nil {
|
||
return nil, nil, err
|
||
}
|
||
|
||
// Ensure we read all the bytes expected
|
||
if n != Size {
|
||
return nil, nil, fmt.Errorf("failed to read %v bytes from crypto/rand: received %v bytes", Size, n)
|
||
}
|
||
// Compute the commitment: HMAC(Sha2, msg, key)
|
||
c, err := ComputeHMAC(sha256.New, msg, d.r[:])
|
||
if err != nil {
|
||
return nil, nil, err
|
||
}
|
||
return c, &d, nil
|
||
}
|
||
|
||
// Open a commitment and return true if the commitment/decommitment pair are valid.
|
||
// reference: spec.§2.4: Commitment Scheme
|
||
func Open(c Commitment, d Witness) (bool, error) {
|
||
// Ensure commitment is well-formed.
|
||
if len(c) != Size {
|
||
return false, fmt.Errorf("invalid commitment, wrong length. %v != %v", len(c), Size)
|
||
}
|
||
|
||
// Re-compute the commitment: HMAC(Sha2, msg, key)
|
||
cʹ, err := ComputeHMAC(sha256.New, d.Msg, d.r[:])
|
||
if err != nil {
|
||
return false, err
|
||
}
|
||
return subtle.ConstantTimeCompare(cʹ, c) == 1, nil
|
||
}
|
||
|
||
// ComputeHMAC computes HMAC(hash_fn, msg, key)
|
||
// Takes in a hash function to use for HMAC
|
||
func ComputeHMAC(f func() hash.Hash, msg []byte, k []byte) ([]byte, error) {
|
||
if f == nil {
|
||
return nil, fmt.Errorf("hash function cannot be nil")
|
||
}
|
||
|
||
mac := hmac.New(f, k)
|
||
w, err := mac.Write(msg)
|
||
|
||
if w != len(msg) {
|
||
return nil, fmt.Errorf("bytes written to hash doesn't match expected: %v != %v", w, len(msg))
|
||
} else if err != nil {
|
||
return nil, err
|
||
}
|
||
return mac.Sum(nil), nil
|
||
}
|