155 lines
2.9 KiB
Go
155 lines
2.9 KiB
Go
package core
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"encoding/base64"
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"errors"
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"math/big"
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"sync"
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)
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// MaxUsed defines the maximum number of Nonces we're willing to hold in
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// memory.
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const MaxUsed = 65536
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const nonceLen = 32
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var errInvalidNonceLength = errors.New("invalid nonce length")
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// NonceService generates, cancels, and tracks Nonces.
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type NonceService struct {
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mu sync.Mutex
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latest int64
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earliest int64
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used map[int64]bool
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gcm cipher.AEAD
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maxUsed int
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}
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// NewNonceService constructs a NonceService with defaults
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func NewNonceService() (*NonceService, error) {
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key := make([]byte, 16)
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if _, err := rand.Read(key); err != nil {
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return nil, err
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}
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c, err := aes.NewCipher(key)
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if err != nil {
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panic("Failure in NewCipher: " + err.Error())
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}
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gcm, err := cipher.NewGCM(c)
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if err != nil {
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panic("Failure in NewGCM: " + err.Error())
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}
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return &NonceService{
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earliest: 0,
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latest: 0,
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used: make(map[int64]bool, MaxUsed),
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gcm: gcm,
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maxUsed: MaxUsed,
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}, nil
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}
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func (ns *NonceService) encrypt(counter int64) (string, error) {
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// Generate a nonce with upper 4 bytes zero
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nonce := make([]byte, 12)
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for i := 0; i < 4; i++ {
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nonce[i] = 0
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}
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if _, err := rand.Read(nonce[4:]); err != nil {
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return "", err
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}
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// Encode counter to plaintext
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pt := make([]byte, 8)
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ctr := big.NewInt(counter)
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pad := 8 - len(ctr.Bytes())
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copy(pt[pad:], ctr.Bytes())
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// Encrypt
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ret := make([]byte, nonceLen)
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ct := ns.gcm.Seal(nil, nonce, pt, nil)
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copy(ret, nonce[4:])
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copy(ret[8:], ct)
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return base64.RawURLEncoding.EncodeToString(ret), nil
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}
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func (ns *NonceService) decrypt(nonce string) (int64, error) {
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decoded, err := base64.RawURLEncoding.DecodeString(nonce)
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if err != nil {
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return 0, err
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}
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if len(decoded) != nonceLen {
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return 0, errInvalidNonceLength
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}
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n := make([]byte, 12)
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for i := 0; i < 4; i++ {
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n[i] = 0
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}
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copy(n[4:], decoded[:8])
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pt, err := ns.gcm.Open(nil, n, decoded[8:], nil)
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if err != nil {
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return 0, err
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}
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ctr := big.NewInt(0)
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ctr.SetBytes(pt)
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return ctr.Int64(), nil
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}
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// Nonce provides a new Nonce.
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func (ns *NonceService) Nonce() (string, error) {
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ns.mu.Lock()
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ns.latest++
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latest := ns.latest
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ns.mu.Unlock()
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return ns.encrypt(latest)
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}
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// minUsed returns the lowest key in the used map. Requires that a lock be held
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// by caller.
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func (ns *NonceService) minUsed() int64 {
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min := ns.latest
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for t := range ns.used {
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if t < min {
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min = t
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}
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}
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return min
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}
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// Valid determines whether the provided Nonce string is valid, returning
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// true if so.
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func (ns *NonceService) Valid(nonce string) bool {
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c, err := ns.decrypt(nonce)
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if err != nil {
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return false
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}
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ns.mu.Lock()
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defer ns.mu.Unlock()
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if c > ns.latest {
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return false
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}
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if c <= ns.earliest {
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return false
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}
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if ns.used[c] {
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return false
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}
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ns.used[c] = true
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if len(ns.used) > ns.maxUsed {
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ns.earliest = ns.minUsed()
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delete(ns.used, ns.earliest)
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}
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return true
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}
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