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SecureW2 Weak Random Seeding for PMS
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SUMMARY
<http://www.securew2.com/uk/> SecureW2 - "powerful open source EAP-TTLS
Client for Windows."
SecureW2 uses weak random number seeding when it generates the PMS (Pre
Master Secret).
DETAILS
Vulnerable Systems:
* SecureW2 versions 3.0 and prior
SecureW2 uses weak random numbers when generating the pre-master-secret.
Vulnerable code:
The code quoted below can be found in
"./Components/Common/release3/version 0/source/CommonTLS.c":
//
// Name: TLSGenPMS
// Description: Generate the 48 random bytes for the PMS (Pre Master
Secret)
// Author: Tom Rixom
// Created: 17 December 2002
//
DWORD
TLSGenPMS( IN OUT BYTE pbPMS[TLS_PMS_SIZE] )
{
int i = 0;
SYSTEMTIME SystemTime;
DWORD dwRet;
dwRet = NO_ERROR;
AA_TRACE( ( TEXT( "TLSGenPMS" ) ) );
pbPMS[0] = 0x03;
pbPMS[1] = 0x01;
//
// Time (DWORD)
//
GetLocalTime( &SystemTime );
srand( ( unsigned int ) SystemTime.wMilliseconds );
//srand( ( unsigned )time( NULL ) );
//
// Random bytes
//
for( i=2; i < TLS_PMS_SIZE; i++ )
pbPMS[i] = ( BYTE ) ( rand() % 255 );
AA_TRACE( ( TEXT( "TLSGenPMS::random bytes: %s" ), AA_ByteToHex(
pbPMS, TLS_PMS_SIZE ) ) );
return dwRet;
}
It appear to be using the weak srand/rand functions seeded by the
milliseconds field from the system clock. That doesn't provide you with
48 bytes of strong randomness, you are lucky to get even a few bytes.
ADDITIONAL INFORMATION
The information has been provided by <mailto:jas@extundo.com> Simon
Josefsson.
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