2.2.1.3.3 Client Security Data (TS_UD_CS_SEC)

The TS_UD_CS_SEC data block contains security-related information used to advertise client cryptographic support. This information is only relevant when Standard RDP Security mechanisms (section 5.3) will be used. See sections 3 and 5.3.2 for a detailed discussion of how this information is used.

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header
encryptionMethods
extEncryptionMethods

header (4 bytes): A GCC user data block header as described in User Data Header (section 2.2.1.3.1). The User Data Header type field MUST be set to CS_SECURITY (0xC002).

encryptionMethods (4 bytes): A 32-bit, unsigned integer. Cryptographic encryption methods supported by the client and used in conjunction with Standard RDP Security. The client MUST specify at least one encryption method, and the server MUST select one of the methods specified by the client. 

Flag	Meaning
40BIT_ENCRYPTION_FLAG 0x00000001	40-bit session keys MUST be used to encrypt data (with RC4) and generate Message Authentication Codes (MAC).
128BIT_ENCRYPTION_FLAG 0x00000002	128-bit session keys MUST be used to encrypt data (with RC4) and generate MACs.
56BIT_ENCRYPTION_FLAG 0x00000008	56-bit session keys MUST be used to encrypt data (with RC4) and generate MACs.
FIPS_ENCRYPTION_FLAG 0x00000010	All encryption and Message Authentication Code generation routines MUST be Federal Information Processing Standard (FIPS) 140-1 compliant.

Section 5.3.2 describes how the client and server negotiate the security parameters for a given connection.

extEncryptionMethods (4 bytes): A 32-bit, unsigned integer. This field is used exclusively for the French locale. In French locale clients, encryptionMethods MUST be set to zero and extEncryptionMethods MUST be set to the value to which encryptionMethods would have been set. For non-French locale clients, this field MUST be set to zero.