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CMSG_KEY_AGREE_ENCRYPT_INFO structure (wincrypt.h)

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The CMSG_KEY_AGREE_ENCRYPT_INFO structure contains encryption information applicable to all key agreement recipients of an enveloped message. The PFN_CMSG_EXPORT_KEY_AGREE function updates this structure.

Syntax

typedef struct _CMSG_KEY_AGREE_ENCRYPT_INFO {
  DWORD                            cbSize;
  DWORD                            dwRecipientIndex;
  CRYPT_ALGORITHM_IDENTIFIER       KeyEncryptionAlgorithm;
  CRYPT_DATA_BLOB                  UserKeyingMaterial;
  DWORD                            dwOriginatorChoice;
  union {
    CERT_ID              OriginatorCertId;
    CERT_PUBLIC_KEY_INFO OriginatorPublicKeyInfo;
  } DUMMYUNIONNAME;
  DWORD                            cKeyAgreeKeyEncryptInfo;
  PCMSG_KEY_AGREE_KEY_ENCRYPT_INFO *rgpKeyAgreeKeyEncryptInfo;
  DWORD                            dwFlags;
} CMSG_KEY_AGREE_ENCRYPT_INFO, *PCMSG_KEY_AGREE_ENCRYPT_INFO;

Members

cbSize

The size, in bytes, of this structure.

dwRecipientIndex

A value that specifies the ordinal number of a recipient in the recipient list specified by the pContentEncryptInfo parameter of the PFN_CMSG_EXPORT_KEY_AGREE function.

KeyEncryptionAlgorithm

A CRYPT_ALGORITHM_IDENTIFIER structure that specifies the algorithm used to encrypt the content encryption key. The CryptMsgOpenToEncode function uses the pszObjId member of the CRYPT_ALGORITHM_IDENTIFIER structure to get the address of the function used to export the key. The function can be installed by using a Cryptography API: Next Generation (CNG) object identifier (OID).

UserKeyingMaterial

A CRYPT_DATA_BLOB structure that contains user keying material provided by the sender to ensure that a different key is generated each time the same two parties generate a pair-wise key.

dwOriginatorChoice

A DWORD that indicates the key identifier to use. This member can be one of the following values.

Value Meaning
CMSG_KEY_AGREE_ORIGINATOR_CERT
 OriginatorCertId
CMSG_KEY_AGREE_ORIGINATOR_PUBLIC_KEY
 OriginatorPublicKeyInfo

DUMMYUNIONNAME

DUMMYUNIONNAME.OriginatorCertId

A CERT_ID structure that identifies the public key of the message originator.

DUMMYUNIONNAME.OriginatorPublicKeyInfo

A CERT_PUBLIC_KEY_INFO structure that contains the public key of the message originator.

cKeyAgreeKeyEncryptInfo

A value that specifies the number of recipients in the rgpKeyAgreeKeyEncryptInfo parameter.

rgpKeyAgreeKeyEncryptInfo

An array of CMSG_KEY_AGREE_KEY_ENCRYPT_INFO structures that contain the encrypted key for each recipient.

dwFlags

A value that specifies what members have been updated, and whose memory allocation must be freed by using the CryptMsgOpenToEncode function.

Value Meaning
CMSG_KEY_AGREE_ENCRYPT_FREE_MATERIAL_FLAG
0x00000002
 The UserKeyingMaterial member was updated.
CMSG_KEY_AGREE_ENCRYPT_FREE_OBJID_FLAG
0x00000020
 The pszObjId member of the CRYPT_ALGORITHM_IDENTIFIER structure referred to by the KeyEncryptionAlgorithm member was updated.
CMSG_KEY_AGREE_ENCRYPT_FREE_PARA_FLAG
0x00000001
 The Parameters member of the CRYPT_ALGORITHM_IDENTIFIER structure referred to by KeyEncryptionAlgorithm member was updated.
CMSG_KEY_AGREE_ENCRYPT_FREE_PUBKEY_ALG_FLAG
0x00000004
 The Algorithm.pszObjId member of the CERT_PUBLIC_KEY_INFO structure referred to by the OriginatorPublicKeyInfo member was updated.
CMSG_KEY_AGREE_ENCRYPT_FREE_PUBKEY_BITS_FLAG
0x00000010
 The PublicKey member of the CERT_PUBLIC_KEY_INFO structure referred to by the OriginatorPublicKeyInfo member was updated.
CMSG_KEY_AGREE_ENCRYPT_FREE_PUBKEY_PARA_FLAG
0x00000008
 The Algorithm.Parameters member of the CERT_PUBLIC_KEY_INFO structure referred to by the OriginatorPublicKeyInfo member was updated.

Remarks

When called with the dwMsgType parameter set to CMSG_ENVELOPED, the CryptMsgOpenToEncode function initializes the CMSG_KEY_AGREE_ENCRYPT_INFO structure from the CMSG_KEY_AGREE_RECIPIENT_ENCODE_INFO structure. The CryptMsgOpenToEncode function calls the PFN_CMSG_EXPORT_KEY_AGREE function to update the CMSG_KEY_AGREE_ENCRYPT_INFO structure. If the callback function cannot be found, the CryptMsgOpenToEncode function fills this structure with default key information from the CMSG_CONTENT_ENCRYPT_INFO structure.

The following members of the CMSG_KEY_AGREE_ENCRYPT_INFO structure can be updated by the callback function:

UserKeyingMaterial
KeyEncryptionAlgorithm.pszObjId
KeyEncryptionAlgorithm.Parameters
dwOriginatorChoice
OriginatorCertId
OriginatorPublicKeyInfo
dwFlags

The other members are read-only.

Requirements

Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header wincrypt.h