Reusing a Nonce, Key Pair in Encryption
Incomplete Base
Structure: Simple
Description
Nonces should be used for the present occasion and only once.
Common Consequences 1
Scope: Access Control
Impact: Bypass Protection MechanismGain Privileges or Assume Identity
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.
Potential Mitigations 2
Phase: Implementation
Refuse to reuse nonce values.
Phase: Implementation
Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
Demonstrative Examples 2
This code takes a password, concatenates it with a nonce, then encrypts it before sending over a network:
Code Example:
Bad
C
cBecause the nonce used is always the same, an attacker can impersonate a trusted party by intercepting and resending the encrypted password. This attack avoids the need to learn the unencrypted password.
This code sends a command to a remote server, using an encrypted password and nonce to prove the command is from a trusted party:
Code Example:
Bad
C++
c++Once again the nonce used is always the same. An attacker may be able to replay previous legitimate commands or execute new arbitrary commands.
References 1
The CLASP Application Security Process
Secure Software, Inc.
2005
ID: REF-18
Likelihood of Exploit
High
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Architecture and Design
Related Weaknesses
Taxonomy Mapping
- CLASP