Class SrtcpCryptoContext

SRTPCryptoContext class is the core class of SRTP implementation. There can be multiple SRTP sources in one SRTP session. And each SRTP stream has a corresponding SRTPCryptoContext object, identified by SSRC. In this way, different sources can be protected independently.

Inheritance

object

SrtcpCryptoContext

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: SipLib.Dtls

Assembly: SipLib.dll

Syntax

public class SrtcpCryptoContext

Constructors

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SrtcpCryptoContext(long)

Constructs an empty SRTPCryptoContext using the SSRC. The other parameters are set to default null value.

Declaration

public SrtcpCryptoContext(long ssrcIn)

Parameters

Type	Name	Description
long	ssrcIn	SSRC of this SRTPCryptoContext

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SrtcpCryptoContext(long, byte[], byte[], SrtpPolicy)

Construct a normal SRTPCryptoContext based on the given parameters.

Declaration

public SrtcpCryptoContext(long ssrcIn, byte[] masterK, byte[] masterS, SrtpPolicy policyIn)

Parameters

Type	Name	Description
long	ssrcIn	The RTP SSRC that this SRTP cryptographic context protects.
byte[]	masterK	byte array holding the master key for this SRTP cryptographic context. Refer to Section 3.2.1 of the RFC about the role of the master key.
byte[]	masterS	byte array holding the master salt for this SRTP cryptographic context.It is used to computer the initialization vector that in turn is input to compute the session key, session authentication key and the session salt.
SrtpPolicy	policyIn	SRTP policy for this SRTP cryptographic context, defined the encryption algorithm, the authentication algorithm, etc

Methods

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Close()

Close the crypto context. The Close function deletes key data and performs a cleanup of the crypto context. Clean up key data, maybe this is the second time.However, sometimes we cannot know if the CryptoContext was used and the application called deriveSrtpKeys(...) that would have cleaned the key data.

Declaration

public void Close()

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DeriveContext(long)

Derives a new SRTPCryptoContext for use with a new SSRC. This method returns a new SRTPCryptoContext initialized with the data of this SRTPCryptoContext. Replacing the SSRC, Roll-over-Counter, and the key derivation rate the application cab use this SRTPCryptoContext to encrypt / decrypt a new stream(Synchronization source) inside one RTP session.

Declaration

public SrtcpCryptoContext DeriveContext(long ssrc)

Parameters

Type	Name	Description
long	ssrc	The SSRC for this context

Returns

Type	Description
SrtcpCryptoContext	Returns a new SRTPCryptoContext with all relevant data set.

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DeriveSrtcpKeys()

Derives the srtcp session keys from the master key.

Declaration

public void DeriveSrtcpKeys()

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GetAuthTagLength()

Gets the authentication tag length of this SRTP cryptographic context

Declaration

public int GetAuthTagLength()

Returns

Type	Description
int

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GetMKILength()

Gets the MKI length of this SRTP cryptographic context

Declaration

public int GetMKILength()

Returns

Type	Description
int

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GetSSRC()

Gets the SSRC of this SRTP cryptographic context

Declaration

public long GetSSRC()

Returns

Type	Description
long

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ProcessPacketAESCM(RawPacket, int)

Performs Counter Mode AES encryption / decryption

Declaration

public void ProcessPacketAESCM(RawPacket pkt, int index)

Parameters

Type	Name	Description
RawPacket	pkt	The RTP packet to be encrypted / decrypted
int	index

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ProcessPacketAESF8(RawPacket, int)

Performs F8 Mode AES encryption / decryption

Declaration

public void ProcessPacketAESF8(RawPacket pkt, int index)

Parameters

Type	Name	Description
RawPacket	pkt	The RTP packet to be encrypted / decrypted
int	index

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ReverseTransformPacket(RawPacket)

Transform a SRTCP packet into a RTCP packet. This method is called when a SRTCP packet was received.

Declaration

public bool ReverseTransformPacket(RawPacket pkt)

Parameters

Type	Name	Description
RawPacket	pkt	The received RTCP packet

Returns

Type	Description
bool	Returns true if the packet can be accepted false if authentication or replay check failed

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TransformPacket(RawPacket)

Transform a RTP packet into a SRTP packet. This method is called when a normal RTP packet ready to be sent.

Operations done by the transformation may include: encryption, using either Counter Mode encryption, or F8 Mode encryption, adding authentication tag, currently HMC SHA1 method.

Both encryption and authentication functionality can be turned off as long as the SRTPPolicy used in this SRTPCryptoContext is requires no encryption and no authentication. Then the packet will be sent out untouched. However this is not encouraged. If no SRTP feature is enabled, then we shall not use SRTP TransformConnector. We should use the original method (RTPManager managed transportation) instead.

Declaration

public void TransformPacket(RawPacket pkt)

Parameters

Type	Name	Description
RawPacket	pkt	The RTP packet that is going to be sent out