127 lines
3.8 KiB
Go
127 lines
3.8 KiB
Go
// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
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// SPDX-License-Identifier: MIT
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package stun
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import ( //nolint:gci
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"crypto/md5" //nolint:gosec
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"crypto/sha1" //nolint:gosec
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"errors"
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"fmt"
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"strings"
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"github.com/pion/stun/internal/hmac"
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)
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// separator for credentials.
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const credentialsSep = ":"
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// NewLongTermIntegrity returns new MessageIntegrity with key for long-term
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// credentials. Password, username, and realm must be SASL-prepared.
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func NewLongTermIntegrity(username, realm, password string) MessageIntegrity {
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k := strings.Join([]string{username, realm, password}, credentialsSep)
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h := md5.New() //nolint:gosec
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fmt.Fprint(h, k)
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return MessageIntegrity(h.Sum(nil))
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}
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// NewShortTermIntegrity returns new MessageIntegrity with key for short-term
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// credentials. Password must be SASL-prepared.
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func NewShortTermIntegrity(password string) MessageIntegrity {
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return MessageIntegrity(password)
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}
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// MessageIntegrity represents MESSAGE-INTEGRITY attribute.
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//
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// AddTo and Check methods are using zero-allocation version of hmac, see
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// newHMAC function and internal/hmac/pool.go.
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//
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// RFC 5389 Section 15.4
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type MessageIntegrity []byte
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func newHMAC(key, message, buf []byte) []byte {
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mac := hmac.AcquireSHA1(key)
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writeOrPanic(mac, message)
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defer hmac.PutSHA1(mac)
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return mac.Sum(buf)
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}
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func (i MessageIntegrity) String() string {
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return fmt.Sprintf("KEY: 0x%x", []byte(i))
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}
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const messageIntegritySize = 20
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// ErrFingerprintBeforeIntegrity means that FINGERPRINT attribute is already in
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// message, so MESSAGE-INTEGRITY attribute cannot be added.
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var ErrFingerprintBeforeIntegrity = errors.New("FINGERPRINT before MESSAGE-INTEGRITY attribute")
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// AddTo adds MESSAGE-INTEGRITY attribute to message.
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//
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// CPU costly, see BenchmarkMessageIntegrity_AddTo.
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func (i MessageIntegrity) AddTo(m *Message) error {
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for _, a := range m.Attributes {
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// Message should not contain FINGERPRINT attribute
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// before MESSAGE-INTEGRITY.
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if a.Type == AttrFingerprint {
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return ErrFingerprintBeforeIntegrity
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}
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}
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// The text used as input to HMAC is the STUN message,
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// including the header, up to and including the attribute preceding the
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// MESSAGE-INTEGRITY attribute.
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length := m.Length
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// Adjusting m.Length to contain MESSAGE-INTEGRITY TLV.
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m.Length += messageIntegritySize + attributeHeaderSize
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m.WriteLength() // writing length to m.Raw
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v := newHMAC(i, m.Raw, m.Raw[len(m.Raw):]) // calculating HMAC for adjusted m.Raw
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m.Length = length // changing m.Length back
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// Copy hmac value to temporary variable to protect it from resetting
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// while processing m.Add call.
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vBuf := make([]byte, sha1.Size)
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copy(vBuf, v)
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m.Add(AttrMessageIntegrity, vBuf)
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return nil
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}
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// ErrIntegrityMismatch means that computed HMAC differs from expected.
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var ErrIntegrityMismatch = errors.New("integrity check failed")
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// Check checks MESSAGE-INTEGRITY attribute.
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//
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// CPU costly, see BenchmarkMessageIntegrity_Check.
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func (i MessageIntegrity) Check(m *Message) error {
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v, err := m.Get(AttrMessageIntegrity)
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if err != nil {
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return err
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}
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// Adjusting length in header to match m.Raw that was
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// used when computing HMAC.
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var (
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length = m.Length
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afterIntegrity = false
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sizeReduced int
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)
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for _, a := range m.Attributes {
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if afterIntegrity {
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sizeReduced += nearestPaddedValueLength(int(a.Length))
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sizeReduced += attributeHeaderSize
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}
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if a.Type == AttrMessageIntegrity {
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afterIntegrity = true
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}
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}
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m.Length -= uint32(sizeReduced)
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m.WriteLength()
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// startOfHMAC should be first byte of integrity attribute.
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startOfHMAC := messageHeaderSize + m.Length - (attributeHeaderSize + messageIntegritySize)
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b := m.Raw[:startOfHMAC] // data before integrity attribute
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expected := newHMAC(i, b, m.Raw[len(m.Raw):])
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m.Length = length
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m.WriteLength() // writing length back
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return checkHMAC(v, expected)
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}
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