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crypto.go
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crypto.go
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package ss2022
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"encoding/base64"
"errors"
"fmt"
"lukechampine.com/blake3"
)
var (
ErrUnknownMethod = errors.New("unknown method")
ErrBadPSKLength = errors.New("PSK length does not meet method requirements")
)
type CipherConfig struct {
// Client: uPSK
// Server: iPSK or uPSK
PSK []byte
// Client: iPSKs
// Server: uPSKs
PSKs [][]byte
// bufferedBlock buffers the block cipher returned by NewBlock.
bufferedBlock cipher.Block
}
func NewCipherConfig(method string, psk []byte, psks [][]byte) (*CipherConfig, error) {
var pskLength int
switch method {
case "2022-blake3-aes-128-gcm":
pskLength = 16
case "2022-blake3-aes-256-gcm":
pskLength = 32
default:
return nil, fmt.Errorf("%w: %s", ErrUnknownMethod, method)
}
if len(psk) != pskLength {
return nil, fmt.Errorf("%w: %s", ErrBadPSKLength, base64.StdEncoding.EncodeToString(psk))
}
for _, psk := range psks {
if len(psk) != pskLength {
return nil, fmt.Errorf("%w: %s", ErrBadPSKLength, base64.StdEncoding.EncodeToString(psk))
}
}
return &CipherConfig{psk, psks, nil}, nil
}
func NewRandomCipherConfig(method string, keySize, eihCount int) (cipherConfig *CipherConfig, err error) {
psk := make([]byte, keySize)
_, err = rand.Read(psk)
if err != nil {
return
}
psks := make([][]byte, eihCount)
for i := range psks {
psks[i] = make([]byte, keySize)
_, err = rand.Read(psks[i])
if err != nil {
return
}
}
cipherConfig, err = NewCipherConfig(method, psk, psks)
return
}
func (c *CipherConfig) NewAEAD(salt []byte) cipher.AEAD {
var key []byte
if len(salt) > 0 {
keyMaterial := make([]byte, len(c.PSK)+len(salt))
copy(keyMaterial, c.PSK)
copy(keyMaterial[len(c.PSK):], salt)
key = make([]byte, len(c.PSK))
blake3.DeriveKey(key, "shadowsocks 2022 session subkey", keyMaterial)
} else {
key = c.PSK
}
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
aead, err := cipher.NewGCM(block)
if err != nil {
panic(err)
}
return aead
}
func (c *CipherConfig) NewShadowStreamCipher(salt []byte) *ShadowStreamCipher {
aead := c.NewAEAD(salt)
nonce := make([]byte, aead.NonceSize())
return &ShadowStreamCipher{
aead: aead,
nonce: nonce,
}
}
func (c *CipherConfig) NewBlock() cipher.Block {
if c.bufferedBlock == nil {
var err error
c.bufferedBlock, err = aes.NewCipher(c.PSK)
if err != nil {
panic(err)
}
}
return c.bufferedBlock
}
// NewTCPIdentityHeaderClientCiphers creates block ciphers for a client TCP session's identity headers.
func (c *CipherConfig) NewTCPIdentityHeaderClientCiphers(salt []byte) []cipher.Block {
ciphers := make([]cipher.Block, len(c.PSKs))
for i := range ciphers {
keyMaterial := make([]byte, len(c.PSKs[i])+len(salt))
copy(keyMaterial, c.PSKs[i])
copy(keyMaterial[len(c.PSKs[i]):], salt)
key := make([]byte, len(c.PSKs[i]))
blake3.DeriveKey(key, "shadowsocks 2022 identity subkey", keyMaterial)
var err error
ciphers[i], err = aes.NewCipher(key)
if err != nil {
panic(err)
}
}
return ciphers
}
// NewTCPIdentityHeaderServerCiphers creates a block cipher for a server TCP session's identity header.
func (c *CipherConfig) NewTCPIdentityHeaderServerCipher(salt []byte) cipher.Block {
// Skip if no uPSKs.
if len(c.PSKs) == 0 {
return nil
}
keyMaterial := make([]byte, len(c.PSK)+len(salt))
copy(keyMaterial, c.PSK)
copy(keyMaterial[len(c.PSK):], salt)
key := make([]byte, len(c.PSK))
blake3.DeriveKey(key, "shadowsocks 2022 identity subkey", keyMaterial)
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
return block
}
// NewUDPIdentityHeaderClientCiphers creates block ciphers for a client UDP service's identity headers.
func (c *CipherConfig) NewUDPIdentityHeaderClientCiphers() []cipher.Block {
ciphers := make([]cipher.Block, len(c.PSKs))
for i := range ciphers {
var err error
ciphers[i], err = aes.NewCipher(c.PSKs[i])
if err != nil {
panic(err)
}
}
return ciphers
}
// NewUDPIdentityHeaderServerCipher creates a block cipher for a server UDP service's identity header.
func (c *CipherConfig) NewUDPIdentityHeaderServerCipher() cipher.Block {
// Skip if no uPSKs.
if len(c.PSKs) == 0 {
return nil
}
return c.NewBlock()
}
// ClientPSKHashes returns the BLAKE3 hashes of c.PSKs[1:] and c.PSK.
func (c *CipherConfig) ClientPSKHashes() [][IdentityHeaderLength]byte {
// Skip if no uPSKs.
if len(c.PSKs) == 0 {
return nil
}
hashes := make([][IdentityHeaderLength]byte, len(c.PSKs))
for i := 1; i < len(c.PSKs); i++ {
hash := blake3.Sum512(c.PSKs[i])
copy(hashes[i-1][:], hash[:])
}
hash := blake3.Sum512(c.PSK)
copy(hashes[len(hashes)-1][:], hash[:])
return hashes
}
// ServerPSKHashMap returns a uPSKHash-*CipherConfig map.
func (c *CipherConfig) ServerPSKHashMap() map[[IdentityHeaderLength]byte]*CipherConfig {
uPSKMap := make(map[[IdentityHeaderLength]byte]*CipherConfig, len(c.PSKs))
for _, psk := range c.PSKs {
hash := blake3.Sum512(psk)
truncatedHash := *(*[IdentityHeaderLength]byte)(hash[:])
uPSKMap[truncatedHash] = &CipherConfig{psk, nil, nil}
}
return uPSKMap
}