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CRYPT_ENCRYPT_MESSAGE_PARA structure (wincrypt.h)

  • Article

The CRYPT_ENCRYPT_MESSAGE_PARA structure contains information used to encrypt messages.

Syntax

typedef struct _CRYPT_ENCRYPT_MESSAGE_PARA {
  DWORD                      cbSize;
  DWORD                      dwMsgEncodingType;
  HCRYPTPROV_LEGACY          hCryptProv;
  CRYPT_ALGORITHM_IDENTIFIER ContentEncryptionAlgorithm;
  void                       *pvEncryptionAuxInfo;
  DWORD                      dwFlags;
  DWORD                      dwInnerContentType;
} CRYPT_ENCRYPT_MESSAGE_PARA, *PCRYPT_ENCRYPT_MESSAGE_PARA;

Members

cbSize

The size, in bytes, of this structure.

dwMsgEncodingType

The type of encoding used. It is always acceptable to specify both the certificate and message encoding types by combining them with a bitwise-OR operation as shown in the following example:

X509_ASN_ENCODING | PKCS_7_ASN_ENCODING

Currently defined encoding types are:

  • X509_ASN_ENCODING
  • PKCS_7_ASN_ENCODING

hCryptProv

This member is not used and should be set to NULL.

Windows Server 2003 and Windows XP:  The handle to the cryptographic service provider (CSP) to be used for encryption. The CSP identified by hCryptProv is used to do content encryption, recipient key encryption, and recipient key export. Its private key is not used.

Unless there is a strong reason for passing in a specific cryptographic provider in hCryptProv, pass zero to use the default RSA or DSS provider.

This member's data type is HCRYPTPROV.

ContentEncryptionAlgorithm

A CRYPT_ALGORITHM_IDENTIFIER structure that contains the object identifier (OID) of the encryption algorithm to use. The CSP specified by the hCryptProv must support this encryption algorithm.

The szOID_OIWSEC_desCBC (CALG_DES) and szOID_RSA_DES_EDE3_CBC (CALG_3DES) encryption algorithms require the Parameters member of this structure to contain an encoded eight-byte initialization vector (IV). If the cbData member of the Parameters member is zero, an Abstract Syntax Notation One (ASN.1)-encoded OCTET STRING that contains the IV is generated using CryptGenRandom. For more information about the KP_IV parameter, see CryptSetKeyParam.

The szOID_NIST_AES128_CBC (BCRYPT_AES_ALGORITHM, 128 bit), szOID_NIST_AES192_CBC (BCRYPT_AES_ALGORITHM, 192 bit), and szOID_NIST_AES256_CBC (BCRYPT_AES_ALGORITHM, 256 bit) encryption algorithms require the Parameters member of this structure to contain an encoded sixteen-byte initialization vector (IV). If the cbData member of the Parameters member is zero, an Abstract Syntax Notation One (ASN.1)-encoded OCTET STRING that contains the IV is generated.

The szOID_RSA_RC2CBC (CALG_RC2) algorithm requires the pbData member of the Parameters member of this structure to be a CRYPT_RC2_CBC_PARAMETERS structure. If the cbData member of the Parameters member is zero, an ASN.1-encoded CRYPT_RC2_CBC_PARAMETERS structure that contains the IV is generated as the pbData member. This generated pbData uses the default dwVersion that corresponds to the 40-bit key length. To override the default 40-bit key length, pvEncryptionAuxInfo can be set to point to a CMSG_RC2_AUX_INFO structure that contains a key bit length.

Note  When a message is decrypted, if it has an initialization vector parameter, the cryptographic message functions call CryptSetKeyParam with the initialization vector before decrypting.
 

pvEncryptionAuxInfo

A pointer to a CMSG_RC2_AUX_INFO structure for RC2 encryption or a CMSG_SP3_COMPATIBLE_AUX_INFO structure for SP3-compatible encryption. For other than RC2 or SP3-compatible encryption, this member must be set to NULL.

If the ContentEncryptionAlgorithm member contains szOID_RSA_RC4, this member points to a CMSG_RC4_AUX_INFO structure that specifies the number of salt bytes to be included.

dwFlags

Normally set to zero. However, if the encoded output is to be a CMSG_ENVELOPED inner content of an outer cryptographic message, such as a CMSG_SIGNED message, the CRYPT_MESSAGE_BARE_CONTENT_OUT_FLAG must be set. If it is not set, content will be encoded as an inner content type of CMSG_DATA.

CRYPT_MESSAGE_ENCAPSULATED_CONTENT_OUT_FLAG can be set to encapsulate non-data inner content within an OCTET STRING before encrypting.

CRYPT_MESSAGE_KEYID_RECIPIENT_FLAG can be set to identify recipients by their Key Identifier and not their Issuer and Serial Number.

dwInnerContentType

Normally set to zero. The dwInnerContentType member must be set to set the cryptographic message types if the input to be encrypted is the encoded output of another cryptographic message such as CMSG_SIGNED.

Requirements

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

See also

CRYPT_ALGORITHM_IDENTIFIER

CryptEncryptMessage

CryptSignAndEncryptMessage