Reusing a nonce, key pair in encryption
From OWASP
This is a Vulnerability. To view all vulnerabilities, please see the Vulnerability Category page.
Contents |
Last revision (mm/dd/yy): 11/6/2008
Description
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
Nonces, are often bundled with a key in a communication exchange to produce a new session key for each exchange.
Risk Factors
TBD
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 Attacks
Related Vulnerabilities
Related Controls
- 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.
Related Technical Impacts
References
TBD
