Difference between revisions of "Reusing a nonce, key pair in encryption"

From OWASP
Jump to: navigation, search
 
Line 1: Line 1:
 
  
 
{{Template:SecureSoftware}}
 
{{Template:SecureSoftware}}
Line 53: Line 52:
 
In C/C++:
 
In C/C++:
  
#include <openssl/sha.h>
+
<pre>
 +
#include <openssl/sha.h>
 
#include <stdio.h>
 
#include <stdio.h>
 
#include <string.h>
 
#include <string.h>
Line 77: Line 77:
 
   return 0;
 
   return 0;
 
}
 
}
 +
</pre>
 +
 
In Java:
 
In Java:
  
 +
<pre>
 
String command = new String("some command to execute")
 
String command = new String("some command to execute")
 
MessageDigest nonce = MessageDigest.getInstance("SHA");
 
MessageDigest nonce = MessageDigest.getInstance("SHA");
Line 88: Line 91:
 
byte[] digest = password.digest();
 
byte[] digest = password.digest();
 
//do somethign with digest//
 
//do somethign with digest//
 +
</pre>
 +
 
==Related problems ==
 
==Related problems ==
  

Revision as of 12:07, 16 April 2006


Overview

Nonces should be used for the present occasion and only once.

Consequences

  • Authentication: Potentially a replay attack, in which an attacker could send the same data twice, could be crafted if nonces are allowed to be reused. This could allow a user to send a message which masquerades as a valid message from a valid user.

Exposure period

  • Design: Mitigating technologies such as safe string libraries and container abstractions could be introduced.
  • Implementation: Many traditional techniques can be used to create a new nonce from different sources.
  • Implementation: Reusing nonces nullifies the use of nonces.

Platform

  • Languages: Any
  • Operating platforms: Any

Required resources

Any

Severity

High

Likelihood of exploit

High

Avoidance and mitigation

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Implementation: Refuse to reuse nonce values.
  • Implementation: Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.

Discussion

Nonces, are often bundled with a key in a communication exchange to produce a new session key for each exchange.

Examples

In C/C++:

#include <openssl/sha.h>
#include <stdio.h>
#include <string.h>
#include <memory.h>

int main(){
  char *paragraph = NULL;
  char *data = NULL;
  char *nonce = "bad";
  char *password = "secret";
  
  parsize=strlen(nonce)+strlen(password);
  paragraph=(char*)malloc(para_size);	
  strncpy(paragraph,nonce,strlen(nonce));
  strcpy(paragraph,password,strlen(password));
  
  data=(unsigned char*)malloc(20);
  SHA1((const unsigned char*)paragraph,parsize,(unsigned char*)data);

  free(paragraph);
  free(data);
//Do something with data//
  return 0;
}

In Java:

String command = new String("some command to execute")
MessageDigest nonce = MessageDigest.getInstance("SHA");
nonce.update(String.valueOf("bad nonce");
byte[] nonce = nonce.digest();

MessageDigest password = MessageDigest.getInstance("SHA");
password.update(nonce + "secretPassword");
byte[] digest = password.digest();
//do somethign with digest//

Related problems

Not available.

Categories