Problem - Kevin Tafuro

HCRYPTKEY SpcGetDerivedKey(HCRYPTPROV hProvider, ALG_ID Algid, LPTSTR password) {
BOOL bResult;
DWORD cbData;
HCRYPTKEY hKey;
HCRYPTHASH hHash;
if (!CryptCreateHash(hProvider, CALG_SHA1, 0, 0, &hHash)) return 0;
cbData = lstrlen(password) * sizeof(TCHAR);
if (!CryptHashData(hHash, (BYTE *)password, cbData, 0)) {
CryptDestroyHash(hHash);
return 0;
}
bResult = CryptDeriveKey(hProvider, Algid, hHash, CRYPT_EXPORTABLE, &hKey);
CryptDestroyHash(hHash);
return (bResult ? hKey : 0);
}
Importing a key with CryptImportKey( ) is, in most cases, just as easy as generating a
new random key. Most often, you’ll be importing data obtained directly from
CryptExportKey( ), so you’ll already have an encrypted key in the form of a
SIMPLEBLOB, as required by CryptImportKey( ). If you need to import raw key data,
things get a whole lot trickier—see Recipe 5.26 for details.
HCRYPTKEY SpcImportKey(HCRYPTPROV hProvider, BYTE *pbData, DWORD dwDataLen,
HCRYPTKEY hPublicKey) {
HCRYPTKEY hKey;
if (!CryptImportKey(hProvider, pbData, dwDataLen, hPublicKey, CRYPT_EXPORTABLE,
&hKey)) return 0;
return hKey;
}
When a key object is created, the cipher to use is tied to that key, and it must be
specified as an argument to either CryptGenKey( ) or CryptDeriveKey( ). It is not
required as an argument by CryptImportKey( ) because the cipher information is
stored as part of the SIMPLEBLOB structure that is required. Table 5-8 lists the symmetric
ciphers that are available using one of the three Microsoft CSPs.
Table 5-8. Symmetric ciphers supported by Microsoft Cryptographic Service Providers
Cipher
Cryptographic
Service Provider ALG_ID constant Key length Block size
RC2 Base, Enhanced,
AES
CALG_RC2 40 bits 64 bits
RC4 Base CALG_RC4 40 bits n/a
RC4 Enhanced, AES CALG_RC4 128 bits n/a
DES Enhanced, AES CALG_DES 56 bits 64 bits
2-key Triple-DES Enhanced, AES CALG_3DES_112 112 bits (effective) 64 bits
3-key Triple-DES Enhanced, AES CALG_3DES 168 bits (effective) 64 bits
AES AES CALG_AES_128 128 bits 128 bits
240 | Chapter 5: Symmetric Encryption
This is the Title of the Book, eMatter Edition
Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.