#Store text messaging program code#

this program must use the certificate of the intended Note: To decrypt the message signed and encrypted here, a BLOB with the name of the receiver is saved in a file.

MyHandleError(TEXT('CryptAcquireCertificatePrivateKey. ')) TEXT('The RDM_TYPE message signer's name is %s '), TEXT('Getting the name of the signer failed. ')) TEXT('The SIMPLE_DISPLAY_TYPE message signer's name is ') values for the second parameter get two different forms of The following two calls to CertGetNameString with different Get and print the name of the message signer. MyHandleError(TEXT('Cert not found. ')) If(!(pSignerCertContext = CertFindCertificateInStore( MyHandleError(TEXT('The MY store could not be opened.')) Note: Case is not significant in certificate store names. For more information, see the CertOpenStore function pReceiverCertContext will be the certificate of the pSignerCertContext will be the certificate of Begin definition of the SignAndEncrypt function. _tprintf(TEXT('Verification failed. ')) _tprintf(TEXT(' The program executed without error. ')) _tprintf(TEXT(' The returned, verified message is -> %s '), encrypted message and also verifies the This function decrypts and displays the Call the local function DecryptAndVerify. ShowBytes(pbSignedAndEncryptedBlob,cbSignedAndEncryptedBlob/4) _tprintf(TEXT('The following is the signed and encrypted ') PbSignedAndEncryptedBlob = SignAndEncrypt( signed and encrypted BLOB and also returns This function returns a pointer to the Call the local function SignAndEncrypt. A DWORD to hold the length of the signed Pointer to a buffer that will hold the LstrlenA((const char *)pbToBeSignedAndEncrypted) + 1 to include the terminating null character. more that the length returned by strlen() This is the length of the message to be

(const unsigned char *)'Insert the message to be signed ' pbToBeSignedAndEncrypted is the message to be Declare and initialize local variables. These functions are defined after main. Declare local functions SignAndEncrypt, DecryptAndVerify, and The local function ShowBytes is declared here and defined after _ftprintf(stderr, TEXT('Program terminating. _ftprintf(stderr, TEXT('Error number %x. '), GetLastError()) _ftprintf(stderr, TEXT('An error occurred in the program. that does more extensive error reporting. For most applications, replace this function with one error (stderr) file and exit the program. handling function, to print an error message to the standard This example uses the function MyHandleError, a simple error Replace the Unicode string below with the certificate subject function to retrieve the certificate of the message signer. SIGNER_NAME is used with the CertFindCertificateInStore #define MY_ENCODING_TYPE (PKCS_7_ASN_ENCODING | X509_ASN_ENCODING) signed message by using a receiver's public key. Signs a message by using a sender's private key and encrypts the

#Store text messaging program code#

The code MyHandleError is included with the example and can also be found along with other auxiliary functions under General Purpose Functions. It also uses MyHandleError to exit the program gracefully in case of any failure. This example uses separate functions to show the signing/encryption process and the decryption/signature-verification process. This example uses the following CryptoAPI functions: All other characters are displayed as the '-' character. The included local function, ShowBytes, displays characters in the buffer with values between '0' and 'z'.

Displaying some of the encrypted contents of a buffer.

For more information, see Retrieving Data of Unknown Length.

Calling a CryptoAPI function to find the required size of a buffer, allocating the buffer of the required size, and calling the CryptoAPI function again to fill the buffer.

Initializing data structures needed to sign, encrypt, decrypt, and verify a message.

Finding and printing the subject name from certificates.

Finding certificates for a message sender and message receiver in the open certificate stores.

Opening and closing system certificate stores.

This example illustrates the following tasks: In addition, the receiver of the message must have access to the private key associated with the public key used to encrypt the message. When the message is signed and encrypted, a certificate belonging to the signer with access to the private key of that signer must be used. Not all of the certificates in a certificate store provide access to the private key associated with that certificate.