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Added support for AES CM 255 crypto suites
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Added support for AES_256_CM_HMAC_SHA1_80 and AES_256_CM_HMAC_SHA1_32
crypto suites.
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@sirzooro
sirzooro committed Jul 12, 2024
1 parent f94600d commit b2a6562
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Showing 5 changed files with 97 additions and 14 deletions.
2 changes: 1 addition & 1 deletion context.go
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,7 @@ func CreateContext(masterKey, masterSalt []byte, profile ProtectionProfile, opts
switch profile {
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
c.cipher, err = newSrtpCipherAeadAesGcm(profile, masterKey, masterSalt)
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
c.cipher, err = newSrtpCipherAesCmHmacSha1(profile, masterKey, masterSalt)
default:
return nil, fmt.Errorf("%w: %#v", errNoSuchSRTPProfile, profile)
Expand Down
8 changes: 4 additions & 4 deletions key_derivation.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,6 @@ func aesCmKeyDerivation(label byte, masterKey, masterSalt []byte, indexOverKdr i
// concatenation of the encryption key label 0x00 with (index DIV kdr),
// - index is 'rollover count' and DIV is 'divided by'

nMasterKey := len(masterKey)
nMasterSalt := len(masterSalt)

prfIn := make([]byte, 16)
Expand All @@ -33,11 +32,12 @@ func aesCmKeyDerivation(label byte, masterKey, masterSalt []byte, indexOverKdr i
return nil, err
}

out := make([]byte, ((outLen+nMasterKey)/nMasterKey)*nMasterKey)
nBlockSize := block.BlockSize()
out := make([]byte, ((outLen+nBlockSize-1)/nBlockSize)*nBlockSize)
var i uint16
for n := 0; n < outLen; n += block.BlockSize() {
for n := 0; n < outLen; n += nBlockSize {
binary.BigEndian.PutUint16(prfIn[len(prfIn)-2:], i)
block.Encrypt(out[n:n+nMasterKey], prfIn)
block.Encrypt(out[n:n+nBlockSize], prfIn)
i++
}
return out[:outLen], nil
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41 changes: 40 additions & 1 deletion key_derivation_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ import (
"github.com/stretchr/testify/assert"
)

func TestValidSessionKeys(t *testing.T) {
func TestValidSessionKeys_AesCm128(t *testing.T) {
masterKey := []byte{0xE1, 0xF9, 0x7A, 0x0D, 0x3E, 0x01, 0x8B, 0xE0, 0xD6, 0x4F, 0xA3, 0x2C, 0x06, 0xDE, 0x41, 0x39}
masterSalt := []byte{0x0E, 0xC6, 0x75, 0xAD, 0x49, 0x8A, 0xFE, 0xEB, 0xB6, 0x96, 0x0B, 0x3A, 0xAB, 0xE6}

Expand Down Expand Up @@ -43,6 +43,45 @@ func TestValidSessionKeys(t *testing.T) {
}
}

func TestValidSessionKeys_AesCm256(t *testing.T) {
masterKey := []byte{
0xf0, 0xf0, 0x49, 0x14, 0xb5, 0x13, 0xf2, 0x76, 0x3a, 0x1b, 0x1f, 0xa1, 0x30, 0xf1, 0x0e, 0x29,
0x98, 0xf6, 0xf6, 0xe4, 0x3e, 0x43, 0x09, 0xd1, 0xe6, 0x22, 0xa0, 0xe3, 0x32, 0xb9, 0xf1, 0xb6,
}
masterSalt := []byte{0x3b, 0x04, 0x80, 0x3d, 0xe5, 0x1e, 0xe7, 0xc9, 0x64, 0x23, 0xab, 0x5b, 0x78, 0xd2}

expectedSessionKey := []byte{
0x5b, 0xa1, 0x06, 0x4e, 0x30, 0xec, 0x51, 0x61, 0x3c, 0xad, 0x92, 0x6c, 0x5a, 0x28, 0xef, 0x73,
0x1e, 0xc7, 0xfb, 0x39, 0x7f, 0x70, 0xa9, 0x60, 0x65, 0x3c, 0xaf, 0x06, 0x55, 0x4c, 0xd8, 0xc4,
}
expectedSessionSalt := []byte{0xfa, 0x31, 0x79, 0x16, 0x85, 0xca, 0x44, 0x4a, 0x9e, 0x07, 0xc6, 0xc6, 0x4e, 0x93}
expectedSessionAuthTag := []byte{0xfd, 0x9c, 0x32, 0xd3, 0x9e, 0xd5, 0xfb, 0xb5, 0xa9, 0xdc, 0x96, 0xb3, 0x08, 0x18, 0x45, 0x4d, 0x13, 0x13, 0xdc, 0x05}

sessionKey, err := aesCmKeyDerivation(labelSRTPEncryption, masterKey, masterSalt, 0, len(masterKey))
if err != nil {
t.Errorf("generateSessionKey failed: %v", err)
} else if !bytes.Equal(sessionKey, expectedSessionKey) {
t.Errorf("Session Key % 02x does not match expected % 02x", sessionKey, expectedSessionKey)
}

sessionSalt, err := aesCmKeyDerivation(labelSRTPSalt, masterKey, masterSalt, 0, len(masterSalt))
if err != nil {
t.Errorf("generateSessionSalt failed: %v", err)
} else if !bytes.Equal(sessionSalt, expectedSessionSalt) {
t.Errorf("Session Salt % 02x does not match expected % 02x", sessionSalt, expectedSessionSalt)
}

authKeyLen, err := ProtectionProfileAes256CmHmacSha1_80.AuthKeyLen()
assert.NoError(t, err)

sessionAuthTag, err := aesCmKeyDerivation(labelSRTPAuthenticationTag, masterKey, masterSalt, 0, authKeyLen)
if err != nil {
t.Errorf("generateSessionAuthTag failed: %v", err)
} else if !bytes.Equal(sessionAuthTag, expectedSessionAuthTag) {
t.Errorf("Session Auth Tag % 02x does not match expected % 02x", sessionAuthTag, expectedSessionAuthTag)
}
}

// This test asserts that calling aesCmKeyDerivation with a non-zero indexOverKdr fails
// Currently this isn't supported, but the API makes sure we can add this in the future
func TestIndexOverKDR(t *testing.T) {
Expand Down
25 changes: 18 additions & 7 deletions protection_profile.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,16 @@ type ProtectionProfile uint16

// Supported protection profiles
// See https://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml
//
// AES128_CM_HMAC_SHA1_80 and AES128_CM_HMAC_SHA1_32 are valid SRTP profiles, but they do not have an DTLS-SRTP Protection Profiles ID assigned
// in RFC 5764. They were in earlier draft of this RFC: https://datatracker.ietf.org/doc/html/draft-ietf-avt-dtls-srtp-03#section-4.1.2
// Their IDs are now marked as reserved in the IANA registry. Despite this Chrome supports them:
// https://chromium.googlesource.com/chromium/deps/libsrtp/+/84122798bb16927b1e676bd4f938a6e48e5bf2fe/srtp/include/srtp.h#694
const (
ProtectionProfileAes128CmHmacSha1_80 ProtectionProfile = 0x0001
ProtectionProfileAes128CmHmacSha1_32 ProtectionProfile = 0x0002
ProtectionProfileAes256CmHmacSha1_80 ProtectionProfile = 0x0003
ProtectionProfileAes256CmHmacSha1_32 ProtectionProfile = 0x0004
ProtectionProfileAeadAes128Gcm ProtectionProfile = 0x0007
ProtectionProfileAeadAes256Gcm ProtectionProfile = 0x0008
)
Expand All @@ -22,7 +29,7 @@ func (p ProtectionProfile) KeyLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAeadAes128Gcm:
return 16, nil
case ProtectionProfileAeadAes256Gcm:
case ProtectionProfileAeadAes256Gcm, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
return 32, nil
default:
return 0, fmt.Errorf("%w: %#v", errNoSuchSRTPProfile, p)
Expand All @@ -32,7 +39,7 @@ func (p ProtectionProfile) KeyLen() (int, error) {
// SaltLen returns length of salt key in bytes.
func (p ProtectionProfile) SaltLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
return 14, nil
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
return 12, nil
Expand All @@ -44,9 +51,9 @@ func (p ProtectionProfile) SaltLen() (int, error) {
// AuthTagRTPLen returns length of RTP authentication tag in bytes for AES protection profiles. For AEAD ones it returns zero.
func (p ProtectionProfile) AuthTagRTPLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_80:
return 10, nil
case ProtectionProfileAes128CmHmacSha1_32:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_32:
return 4, nil
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
return 0, nil
Expand All @@ -58,7 +65,7 @@ func (p ProtectionProfile) AuthTagRTPLen() (int, error) {
// AuthTagRTCPLen returns length of RTCP authentication tag in bytes for AES protection profiles. For AEAD ones it returns zero.
func (p ProtectionProfile) AuthTagRTCPLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
return 10, nil
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
return 0, nil
Expand All @@ -70,7 +77,7 @@ func (p ProtectionProfile) AuthTagRTCPLen() (int, error) {
// AEADAuthTagLen returns length of authentication tag in bytes for AEAD protection profiles. For AES ones it returns zero.
func (p ProtectionProfile) AEADAuthTagLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
return 0, nil
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
return 16, nil
Expand All @@ -82,7 +89,7 @@ func (p ProtectionProfile) AEADAuthTagLen() (int, error) {
// AuthKeyLen returns length of authentication key in bytes for AES protection profiles. For AEAD ones it returns zero.
func (p ProtectionProfile) AuthKeyLen() (int, error) {
switch p {
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80:
case ProtectionProfileAes128CmHmacSha1_32, ProtectionProfileAes128CmHmacSha1_80, ProtectionProfileAes256CmHmacSha1_32, ProtectionProfileAes256CmHmacSha1_80:
return 20, nil
case ProtectionProfileAeadAes128Gcm, ProtectionProfileAeadAes256Gcm:
return 0, nil
Expand All @@ -98,6 +105,10 @@ func (p ProtectionProfile) String() string {
return "SRTP_AES128_CM_HMAC_SHA1_80"
case ProtectionProfileAes128CmHmacSha1_32:
return "SRTP_AES128_CM_HMAC_SHA1_32"
case ProtectionProfileAes256CmHmacSha1_80:
return "SRTP_AES256_CM_HMAC_SHA1_80"
case ProtectionProfileAes256CmHmacSha1_32:
return "SRTP_AES256_CM_HMAC_SHA1_32"
case ProtectionProfileAeadAes128Gcm:
return "SRTP_AEAD_AES_128_GCM"
case ProtectionProfileAeadAes256Gcm:
Expand Down
35 changes: 34 additions & 1 deletion srtp_cipher_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,39 @@ func createTestCiphers() []testCipher {
0x37, 0xff, 0x64, 0xe5, 0xcb, 0xd2,
},
},
{
profile: ProtectionProfileAes256CmHmacSha1_32,
encryptedRTPPacket: []byte{
0x80, 0x0f, 0x12, 0x34, 0xde, 0xca, 0xfb, 0xad,
0xca, 0xfe, 0xba, 0xbe, 0xac, 0x3b, 0xca, 0x88,
0x14, 0x37, 0x57, 0x83, 0x35, 0xc6, 0xd4, 0x57,
0xf1, 0xc3, 0x6b, 0xa7, 0x3d, 0x71, 0x48, 0x63,
},
encryptedRTCPPacket: []byte{
0x81, 0xc8, 0x00, 0x0b, 0xca, 0xfe, 0xba, 0xbe,
0x97, 0x04, 0x31, 0xdc, 0x4a, 0xe6, 0xd2, 0xaf,
0xd6, 0x54, 0xbf, 0x90, 0xf4, 0x35, 0x44, 0x9e,
0x80, 0x00, 0x00, 0x01, 0xbf, 0x18, 0x18, 0x2d,
0xd1, 0x18, 0x81, 0x28, 0x78, 0xb1,
},
},
{
profile: ProtectionProfileAes256CmHmacSha1_80,
encryptedRTPPacket: []byte{
0x80, 0x0f, 0x12, 0x34, 0xde, 0xca, 0xfb, 0xad,
0xca, 0xfe, 0xba, 0xbe, 0xac, 0x3b, 0xca, 0x88,
0x14, 0x37, 0x57, 0x83, 0x35, 0xc6, 0xd4, 0x57,
0xf1, 0xc3, 0x6b, 0xa7, 0x3d, 0x71, 0x48, 0x63,
0x90, 0x9b, 0xbf, 0x15, 0xac, 0xec,
},
encryptedRTCPPacket: []byte{
0x81, 0xc8, 0x00, 0x0b, 0xca, 0xfe, 0xba, 0xbe,
0x97, 0x04, 0x31, 0xdc, 0x4a, 0xe6, 0xd2, 0xaf,
0xd6, 0x54, 0xbf, 0x90, 0xf4, 0x35, 0x44, 0x9e,
0x80, 0x00, 0x00, 0x01, 0xbf, 0x18, 0x18, 0x2d,
0xd1, 0x18, 0x81, 0x28, 0x78, 0xb1,
},
},
{
profile: ProtectionProfileAeadAes128Gcm,
encryptedRTPPacket: []byte{
Expand Down Expand Up @@ -104,7 +137,7 @@ func createTestCiphers() []testCipher {
}
masterSalt := []byte{
0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
0xa8, 0xa9, 0xaa, 0xab, 0x0ac, 0xad,
0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad,
}
decryptedRTPPacket := []byte{
0x80, 0x0f, 0x12, 0x34, 0xde, 0xca, 0xfb, 0xad,
Expand Down

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