cryptEncrypt never returns the same ciphertext twice

[othman taj via .NET 247]

Hi everyone,

I want to encrypt and decrypt a message. I'm using RSA encryption/decryption with PRIVATEKEYBLOB, no hash, and everything works fine, ie I can see my plaintext.

I notices that cryptEncrypt in cryptoAPI never returns the same ciphertext, can anyone explain me why ?
Thanks a lot,

Othman

--------------------------------
From: othman taj

-----------------------
Posted by a user from .NET 247 (http://www.dotnet247.com/)

<Id>mDmY2PMFqE+kVmaJoX3vXA==</Id>

[Aaron Fischer]

this is because your Initilization vector and key are are getting generated
on every call that you make. after your first call you need to rember these
two values, so that you can use them again in a later call.

[othman taj]

In Fact, I'm using always the same key, ie I import my key and crypt with
this one. Also the initialization vector isn't related to the asymetric
encryption scheme (I'm using RSA). So why cryptEncrypt returns different
ciphertexts with the same key used, each time ?

"Aaron Fischer" wrote:

this is because your Initilization vector and key are are getting generated
on every call that you make. after your first call you need to rember these
two values, so that you can use them again in a later call.

[Jon Skeet [C# MVP]]

<"=?Utf-8?B?b3RobWFuIHRhag==?=" <othman
ta*@discussions.microsoft.com>> wrote:

In Fact, I'm using always the same key, ie I import my key and crypt with
this one. Also the initialization vector isn't related to the asymetric
encryption scheme (I'm using RSA). So why cryptEncrypt returns different
ciphertexts with the same key used, each time ?

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Othman]

Here's my code. i couldn't make it shorter :)

As you can see I fill a private key blob with my previously generated RSA
keys. I write this keyBLOB to a file. Then I crypt a msg with the keyBLOB and
decrypt it. the result of encryption is always different.

Thanks you for help

bool WriteKeyToFile()
{
HCRYPTKEY hKey = 0;
HCRYPTPROV hProv = 0;
PBYTE pbKeyBlob = NULL;
DWORD mod_size = 128;
DWORD publicExponent = 65537;

unsigned char *modulus = new unsigned char[128];
unsigned char *prime1 = new unsigned char[64];
unsigned char *prime2 = new unsigned char[64];
unsigned char *exponent1 =new unsigned char[64];
unsigned char *exponent2 = new unsigned char[64];
unsigned char *coefficient = new unsigned char[64];
unsigned char *privateExponent = new unsigned char[128];

pbKeyBlob = (unsigned char*)malloc(sizeof(PUBLICKEYSTRUC) +
sizeof(RSAPUBKEY) + mod_size + (mod_size/2 * 7));
unsigned char *pKeybuf;
pKeybuf = (pbKeyBlob) + sizeof(PUBLICKEYSTRUC) + sizeof(RSAPUBKEY) ;

RSAPUBKEY *pRsaPubKey = 0;
BLOBHEADER *blobHeader;
blobHeader = (PUBLICKEYSTRUC*)pbKeyBlob;
blobHeader->bType = PRIVATEKEYBLOB;
blobHeader->bVersion = 0x02;
blobHeader->reserved = 0;
blobHeader->aiKeyAlg = CALG_RSA_KEYX;
pRsaPubKey = (RSAPUBKEY*)(((unsigned char*)pbKeyBlob) +
sizeof(PUBLICKEYSTRUC));
pRsaPubKey->magic = 0x32415352;
pRsaPubKey->bitlen = mod_size * 8;
pRsaPubKey->pubexp = publicExponent;

FILE *fKeys = fopen("\\KEYS", "rb");
unsigned char* bufferKeys = new unsigned char[576];
fread(bufferKeys, 1,576 , fKeys);

memcpy(modulus, bufferKeys, 128);
bufferKeys += 128;
memcpy(prime1,bufferKeys,64);
bufferKeys += 64;
memcpy(prime2,bufferKeys,64);
bufferKeys += 64;
memcpy(exponent1,bufferKeys,64);
bufferKeys += 64;
memcpy(exponent2,bufferKeys,64);
bufferKeys += 64;
memcpy(coefficient,bufferKeys,64);
bufferKeys += 64;
memcpy(privateExponent,bufferKeys, 128);
bufferKeys += 128;

memcpy(pKeybuf, modulus, 128);
bufferKeys += 128;
memcpy(pKeybuf,prime1,64);
bufferKeys += 64;
memcpy(pKeybuf,prime2,64);
bufferKeys += 64;
memcpy(pKeybuf,exponent1,64);
bufferKeys += 64;
memcpy(pKeybuf,exponent2,64);
bufferKeys += 64;
memcpy(pKeybuf,coefficient,64);
bufferKeys += 64;
memcpy(pKeybuf,privateExponent, 128);
bufferKeys += 128;

DWORD dwBlobLen = sizeof(PUBLICKEYSTRUC) + sizeof(RSAPUBKEY) + mod_size +
(mod_size/2 * 7);
if(!CryptAcquireContext(&hProv, MS_ENHANCED_PROV , NULL, PROV_RSA_FULL, 0))
return false;

if(!CryptImportKey(hProv, pbKeyBlob,
sizeof(PUBLICKEYSTRUC)+sizeof(RSAPUBKEY)+mod_size+ (mod_size/2 * 7), 0,0,
&hKey))
return false;

FILE *fIn = fopen("\\BLOBKey", "wb+");
if (fIn == NULL)
return false;

fwrite(pbKeyBlob, 1, dwBlobLen, fIn);
if((hKey != 0) && (hProv != 0))
{
if(!CryptDestroyKey(hKey))
return false;
if(!CryptReleaseContext(hProv, 0))
return false;
}

fclose(fIn);
return true;
}

bool CryptDecrypt()
{
HCRYPTPROV hProv;
HCRYPTKEY hKey;
DWORD dwBlobLen = 596; // length of PRIVATEKEYBLOB
BYTE *pbKeyBlob = NULL;
BYTE[128] = "123456789012345678901234";

if ((pbKeyBlob = (PBYTE)malloc(dwBlobLen))==NULL)
return false;

FILE *fIn = fopen("\\BLOBKey", "rb");
fread(pbKeyBlob, 1,dwBlobLen , fIn);

if(!CryptAcquireContext(&hProv, MS_ENHANCED_PROV, NULL, PROV_RSA_FULL, 0))
return false;
if(!CryptImportKey(hProv, pbKeyBlob, dwBlobLen, 0, 0, &hKey))
return false;
dwDataLen = 24;
if(!CryptEncrypt(hKey, 0,TRUE, 0, AESKey, &dwDataLen, (DWORD)sizeof(AESKey)))
return false;
if (!CryptDecrypt(hKey, 0, TRUE, 0, AESKey, &dwDataLen))
return false;
if((hKey != 0) && (hProv != 0))
{
if(!CryptDestroyKey(hKey))
return false;
if(!CryptReleaseContext(hProv, 0))
return false;
}

fclose(fIn);
fclose(fIn1);
return false;
}

"Jon Skeet [C# MVP]" wrote:

<"=?Utf-8?B?b3RobWFuIHRhag==?=" <othman
ta*@discussions.microsoft.com>> wrote:

In Fact, I'm using always the same key, ie I import my key and crypt with
this one. Also the initialization vector isn't related to the asymetric
encryption scheme (I'm using RSA). So why cryptEncrypt returns different
ciphertexts with the same key used, each time ?

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Jon Skeet [C# MVP]]

Othman <Ot****@discussions.microsoft.com> wrote:

Here's my code. i couldn't make it shorter :)

That's not C# code. (It's not complete, either, but that's another
issue.) I assumed you were writing in C#, given the newsgroup. If
you're writing in C, I suggest you use a C newsgroup.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too