Man page - cryptocontext(3)
Packages contains this manual
- rtppkt.h(3)
- cqueue(3)
- formats.h(3)
- private.h(3)
- sockets(3)
- queuebase.h(3)
- sessions(3)
- ioqueue(3)
- oqueue.h(3)
- rtppacket(3)
- ext.h(3)
- cqueue.h(3)
- base.h(3)
- rtpext(3)
- rtp.h(3)
- sources.h(3)
- iqueue(3)
- pool.h(3)
- queuebase(3)
- channel.h(3)
- sources(3)
- iqueue.h(3)
- ioqueue.h(3)
- payload(3)
- rtcppacket(3)
- rtcppkt.h(3)
- oqueue(3)
apt-get install libccrtp-doc
Manual
CryptoContext
NAMESYNOPSIS
Public Member Functions
Detailed Description
Constructor & Destructor Documentation
CryptoContext::CryptoContext (uint32 ssrc)
CryptoContext::CryptoContext (uint32 ssrc, int32 roc, int64 keyDerivRate,const int32 ealg, const int32 aalg, uint8 * masterKey, int32masterKeyLength, uint8 * masterSalt, int32 masterSaltLength, int32ekeyl, int32 akeyl, int32 skeyl, int32 tagLength)
CryptoContext::˜CryptoContext ()
Member Function Documentation
bool CryptoContext::checkReplay (uint16 newSeqNumber)
void CryptoContext::deriveSrtpKeys (uint64 index)
int32 CryptoContext::getMkiLength () const [inline]
uint32 CryptoContext::getRoc () const [inline]
uint32 CryptoContext::getSsrc () const [inline]
int32 CryptoContext::getTagLength () const [inline]
uint64 CryptoContext::guessIndex (uint16 newSeqNumber)
CryptoContext * CryptoContext::newCryptoContextForSSRC (uint32 ssrc, introc, int64 keyDerivRate)
void CryptoContext::setRoc (uint32 r) [inline]
void CryptoContext::srtpAuthenticate (RTPPacket * rtp, uint32 roc, uint8 *tag)
void CryptoContext::srtpEncrypt (RTPPacket * rtp, uint64 index, uint32ssrc)
void CryptoContext::update (uint16 newSeqNumber)
Author
NAME
CryptoContext - The implementation for a SRTP cryptographic context.
SYNOPSIS
#include <CryptoContext.h>
Public Member Functions
CryptoContext
(uint32 ssrc)
Constructor for empty SRTP cryptographic context.
CryptoContext
(uint32 ssrc, int32 roc, int64
keyDerivRate, const int32 ealg, const int32 aalg, uint8
*masterKey, int32 masterKeyLength, uint8 *masterSalt, int32
masterSaltLength, int32 ekeyl, int32 akeyl, int32 skeyl,
int32 tagLength)
Constructor for an active SRTP cryptographic context.
˜CryptoContext
()
Destructor.
void
setRoc
(uint32 r)
Set the Roll-Over-Counter.
uint32
getRoc
() const
Get the Roll-Over-Counter.
void
srtpEncrypt
(
RTPPacket
*rtp, uint64
index, uint32 ssrc)
Perform SRTP encryption.
void
srtpAuthenticate
(
RTPPacket
*rtp, uint32
roc, uint8 *tag)
Compute the authentication tag.
void
deriveSrtpKeys
(uint64 index)
Perform key derivation according to SRTP specification.
uint64
guessIndex
(uint16 newSeqNumber)
Compute (guess) the new SRTP index based on the sequence
number of a received RTP packet.
bool
checkReplay
(uint16 newSeqNumber)
Check for packet replay.
void
update
(uint16 newSeqNumber)
Update the SRTP packet index.
int32
getTagLength
() const
Get the length of the SRTP authentication tag in bytes.
int32
getMkiLength
() const
Get the length of the MKI in bytes.
uint32
getSsrc
() const
Get the SSRC of this SRTP Cryptograhic context.
CryptoContext
*
newCryptoContextForSSRC
(uint32
ssrc, int roc, int64 keyDerivRate)
Derive a new Crypto Context for use with a new SSRC.
Detailed Description
The implementation for a SRTP cryptographic context.
This class holds data and provides functions that implement a cryptographic context for SRTP, Refer to RFC 3711, chapter 3.2 for some more detailed information about the SRTP cryptographic context.
Each SRTP cryptographic context maintains a RTP source identified by its SSRC. Thus you can independently protect each source inside a RTP session.
Key management mechanisms negotiate the parameters for the SRTP cryptographic context, such as master key, key length, authentication length and so on. The key management mechanisms are not part of SRTP. Refer to MIKEY (RFC 3880) or to Phil Zimmermann’s ZRTP protocol (draft-zimmermann-avt-zrtp-01). After key management negotiated the data the application can setup the SRTP cryptographic context and enable SRTP processing.
Currently this implementation supports RTP only, not RTCP.
Author
Israel Abad i_abad@terra.es
Erik Eliasson eliasson@it.kth.se
Johan Bilien jobi@via.ecp.fr
Joachim Orrblad joachim@orrblad.com
Werner Dittmann Werner.Dittmann@t-online.de
Constructor & Destructor Documentation
CryptoContext::CryptoContext (uint32 ssrc)
Constructor for empty SRTP cryptographic context. This constructor creates an empty SRTP cryptographic context were all algorithms are set to the null algorithm, that is no SRTP processing is performed.
Parameters
ssrc The RTP SSRC that this SRTP cryptographic context protects.
CryptoContext::CryptoContext (uint32 ssrc, int32 roc, int64 keyDerivRate,const int32 ealg, const int32 aalg, uint8 * masterKey, int32masterKeyLength, uint8 * masterSalt, int32 masterSaltLength, int32ekeyl, int32 akeyl, int32 skeyl, int32 tagLength)
Constructor for an active SRTP cryptographic context. This constructor creates an active SRTP cryptographic context were algorithms are enabled, keys are computed and so on. This SRTP cryptographic context can protect a RTP SSRC stream.
Parameters
ssrc
The RTP SSRC that
this SRTP cryptographic context protects.
roc
The initial Roll-Over-Counter according to RFC 3711.
These are the upper 32 bit of the overall 48 bit SRTP packet
index. Refer to chapter 3.2.1 of the RFC.
keyDerivRate
The key derivation rate defines when to
recompute the SRTP session keys. Refer to chapter 4.3.1 in
the RFC.
ealg
The encryption algorithm to use. Possible values
are
SrtpEncryptionNull, SrtpEncryptionAESCM,
SrtpEncryptionAESF8
. See chapter 4.1.1 for AESCM
(Counter mode) and 4.1.2 for AES F8 mode.
aalg
The authentication algorithm to use. Possible
values are
SrtpEncryptionNull,
SrtpAuthenticationSha1Hmac
. The only active algorithm
here is SHA1 HMAC, a SHA1 based hashed message
authentication code as defined in RFC 2104.
masterKey
Pointer to the master key for this SRTP
cryptographic context. Must point to
masterKeyLength
bytes. Refer to chapter 3.2.1 of
the RFC about the role of the master key.
masterKeyLength
The length in bytes of the master key in
bytes. The length must match the selected encryption
algorithm. Because SRTP uses AES based encryption only, then
master key length may be 16 or 32 bytes (128 or 256 bit
master key)
masterSalt
SRTP uses the master salt to computer the
initialization vector that in turn is input to compute the
session key, session authentication key and the session
salt.
masterSaltLength
The length in bytes of the master salt
data in bytes. SRTP uses AES as encryption algorithm. AES
encrypts 16 byte blocks (independent of the key length).
According to RFC3711 the standard value for the master salt
length should be 112 bit (14 bytes).
ekeyl
The length in bytes of the session encryption key
that SRTP shall compute and use. Usually the same length as
for the master key length. But you may use a different
length as well. Be carefull that the key management
mechanisms supports different key lengths.
akeyl
The length in bytes of the session authentication
key. SRTP computes this key and uses it as input to the
authentication algorithm. The standard value is 160 bits (20
bytes).
skeyl
The length in bytes of the session salt. SRTP
computes this salt key and uses it as input during
encryption. The length usually is the same as the master
salt length.
tagLength
The length is bytes of the authentication tag
that SRTP appends to the RTP packet. Refer to chapter 4.2.
in the RFC 3711.
CryptoContext::˜CryptoContext ()
Destructor. Cleans the SRTP cryptographic context.
Member Function Documentation
bool CryptoContext::checkReplay (uint16 newSeqNumber)
Check for packet replay. The method check if a received packet is either to old or was already received.
The method supports a 64 packet history relative the the given sequence number.
Parameters
newSeqNumber The sequence number of the received RTP packet in host order.
Returns
true if no replay, false if packet is too old ar was already received.
void CryptoContext::deriveSrtpKeys (uint64 index)
Perform key derivation according to SRTP specification. This method computes the session key, session authentication key and the session salt key. This method must be called at least once after the SRTP Cryptograhic context was set up.
Parameters
index The 48 bit SRTP packet index. See the guessIndex method.
int32 CryptoContext::getMkiLength () const [inline]
Get the length of the MKI in bytes.
Returns
the length of the MKI.
uint32 CryptoContext::getRoc () const [inline]
Get the Roll-Over-Counter. Ths method get the upper 32 bit of the 48 bit SRTP packet index (the roll-over-part)
Returns
The roll-over-counter
uint32 CryptoContext::getSsrc () const [inline]
Get the SSRC of this SRTP Cryptograhic context.
Returns
the SSRC.
int32 CryptoContext::getTagLength () const [inline]
Get the length of the SRTP authentication tag in bytes.
Returns
the length of the authentication tag.
uint64 CryptoContext::guessIndex (uint16 newSeqNumber)
Compute (guess) the new SRTP index based on the sequence number of a received RTP packet. The method uses the algorithm show in RFC3711, Appendix A, to compute the new index.
Parameters
newSeqNumber The sequence number of the received RTP packet in host order.
Returns
The new SRTP packet index
CryptoContext * CryptoContext::newCryptoContextForSSRC (uint32 ssrc, introc, int64 keyDerivRate)
Derive a new Crypto Context for use with a new SSRC. This method returns a new Crypto Context initialized with the data of this crypto context. Replacing the SSRC, Roll-over-Counter, and the key derivation rate the application cab use this Crypto Context to encrypt / decrypt a new stream (Synchronization source) inside one RTP session.
Before the application can use this crypto context it must call the deriveSrtpKeys method.
Parameters
ssrc
The SSRC for this
context
roc
The Roll-Over-Counter for this context
keyDerivRate
The key derivation rate for this
context
Returns
a new CryptoContext with all relevant data set.
void CryptoContext::setRoc (uint32 r) [inline]
Set the Roll-Over-Counter. Ths method sets the upper 32 bit of the 48 bit SRTP packet index (the roll-over-part)
Parameters
r The roll-over-counter
void CryptoContext::srtpAuthenticate (RTPPacket * rtp, uint32 roc, uint8 *tag)
Compute the authentication tag. Compute the authentication tag according the the parameters in the SRTP Cryptograhic context.
Parameters
rtp
The RTP packet that
contains the data to authenticate.
roc
The 32 bit SRTP roll-over-counter.
tag
Points to a buffer that hold the computed tag. This
buffer must be able to hold
tagLength
bytes.
void CryptoContext::srtpEncrypt (RTPPacket * rtp, uint64 index, uint32ssrc)
Perform SRTP encryption. This method encrypts and decrypts SRTP payload data. Plain data gets encrypted, encrypted data get decrypted.
Parameters
rtp
The RTP packet that
contains the data to encrypt.
index
The 48 bit SRTP packet index. See the
guessIndex
method.
ssrc
The RTP SSRC data in
host
order.
void CryptoContext::update (uint16 newSeqNumber)
Update the SRTP packet index. Call this method after all checks were successful. See chapter 3.3.1 in the RFC when to update the ROC and ROC processing.
Parameters
newSeqNumber The sequence number of the received RTP packet in host order.
Author
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