status-im/status-go

package encryption

import (
    "crypto/aes"
    "crypto/cipher"
    "crypto/ecdsa"
    "crypto/rand"
    "encoding/binary"
    "errors"
    "io"
    "time"

    "github.com/status-im/status-go/eth-node/crypto"
    "github.com/status-im/status-go/eth-node/crypto/ecies"
)

const keyBumpValue = uint64(10)

// GetCurrentTime64 returns the current unix time in milliseconds
func GetCurrentTime() uint64 {
    return (uint64)(time.Now().UnixMilli())
}

// bumpKeyID takes a timestampID and returns its value incremented by the keyBumpValue
func bumpKeyID(timestampID uint64) uint64 {
    return timestampID + keyBumpValue
}

func generateHashRatchetKeyID(groupID []byte, timestamp uint64, keyBytes []byte) []byte {
    var keyMaterial []byte

    keyMaterial = append(keyMaterial, groupID...)

    timestampBytes := make([]byte, 8) // 8 bytes for a uint64
    binary.LittleEndian.PutUint64(timestampBytes, timestamp)
    keyMaterial = append(keyMaterial, timestampBytes...)

    keyMaterial = append(keyMaterial, keyBytes...)

    return crypto.Keccak256(keyMaterial)
}

func publicKeyMostRelevantBytes(key *ecdsa.PublicKey) uint32 {

    keyBytes := crypto.FromECDSAPub(key)

    return binary.LittleEndian.Uint32(keyBytes[1:5])
}

func encrypt(plaintext []byte, key []byte, reader io.Reader) ([]byte, error) {
    c, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }

    gcm, err := cipher.NewGCM(c)
    if err != nil {
        return nil, err
    }

    nonce := make([]byte, gcm.NonceSize())
    if _, err = io.ReadFull(reader, nonce); err != nil {
        return nil, err
    }

    return gcm.Seal(nonce, nonce, plaintext, nil), nil
}

func GenerateSharedKey(privateKey *ecdsa.PrivateKey, publicKey *ecdsa.PublicKey) ([]byte, error) {

    const encryptedPayloadKeyLength = 16

    return ecies.ImportECDSA(privateKey).GenerateShared(
        ecies.ImportECDSAPublic(publicKey),
        encryptedPayloadKeyLength,
        encryptedPayloadKeyLength,
    )
}

func buildGroupRekeyMessage(privateKey *ecdsa.PrivateKey, groupID []byte, timestamp uint64, keyMaterial []byte, keys []*ecdsa.PublicKey) (*RekeyGroup, error) {

    message := &RekeyGroup{
        Timestamp: timestamp,
    }

    message.Keys = make(map[uint32][]byte)

    for _, k := range keys {

        sharedKey, err := GenerateSharedKey(privateKey, k)
        if err != nil {
            return nil, err
        }

        encryptedKey, err := encrypt(keyMaterial, sharedKey, rand.Reader)
        if err != nil {
            return nil, err
        }

        kBytes := publicKeyMostRelevantBytes(k)

        if message.Keys[kBytes] == nil {
            message.Keys[kBytes] = encryptedKey
        } else {
            message.Keys[kBytes] = append(message.Keys[kBytes], encryptedKey...)
        }
    }

    return message, nil
}

const nonceLength = 12

func decrypt(cyphertext []byte, key []byte) ([]byte, error) {
    if len(cyphertext) < nonceLength {
        return nil, errors.New("invalid cyphertext length")
    }

    c, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }

    gcm, err := cipher.NewGCM(c)
    if err != nil {
        return nil, err
    }

    nonce := cyphertext[:nonceLength]
    return gcm.Open(nil, nonce, cyphertext[nonceLength:], nil)
}

const keySize = 60

func decryptGroupRekeyMessage(privateKey *ecdsa.PrivateKey, publicKey *ecdsa.PublicKey, message *RekeyGroup) ([]byte, error) {
    kBytes := publicKeyMostRelevantBytes(&privateKey.PublicKey)
    if message.Keys == nil || message.Keys[kBytes] == nil {
        return nil, nil
    }

    sharedKey, err := GenerateSharedKey(privateKey, publicKey)
    if err != nil {
        return nil, err
    }

    keys := message.Keys[kBytes]

    nKeys := len(keys) / keySize

    var decryptedKey []byte
    for i := 0; i < nKeys; i++ {

        encryptedKey := keys[i*keySize : i*keySize+keySize]
        decryptedKey, err = decrypt(encryptedKey, sharedKey)
        if err != nil {
            continue
        } else {
            break
        }

    }

    return decryptedKey, nil
}