CWE - CWE-329: Not Using a Random IV with CBC Mode (2.11)

Weakness ID: 329

Abstraction: Variant

Status: Draft

Presentation Filter:

Description

Description Summary

Not using a random initialization Vector (IV) with Cipher Block Chaining (CBC) Mode causes algorithms to be susceptible to dictionary attacks.

Time of Introduction

Architecture and Design
Implementation

Applicable Platforms

Languages

All

Common Consequences

Scope	Effect
Confidentiality Other	Technical Impact: Read application data; Other If the CBC is not properly initialized, data that is encrypted can be compromised and therefore be read.
Integrity	Technical Impact: Modify application data If the CBC is not properly initialized, encrypted data could be tampered with in transfer.
Access Control Other	Technical Impact: Bypass protection mechanism; Other Cryptographic based authentication systems could be defeated.

Likelihood of Exploit

Medium

Demonstrative Examples

Example 1

In the following examples, CBC mode is used when encrypting data:

(Bad Code)

Example Languages: C and C++

EVP_CIPHER_CTX ctx;

char key[EVP_MAX_KEY_LENGTH];

char iv[EVP_MAX_IV_LENGTH];

RAND_bytes(key, b);

memset(iv,0,EVP_MAX_IV_LENGTH);

EVP_EncryptInit(&ctx,EVP_bf_cbc(), key,iv);

(Bad Code)

Example Language: Java

public class SymmetricCipherTest {

public static void main() {

byte[] text ="Secret".getBytes();

byte[] iv ={

0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00

};

KeyGenerator kg = KeyGenerator.getInstance("DES");

kg.init(56);

SecretKey key = kg.generateKey();

Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");

IvParameterSpec ips = new IvParameterSpec(iv);

cipher.init(Cipher.ENCRYPT_MODE, key, ips);

return cipher.doFinal(inpBytes);

}

In both of these examples, the initialization vector (IV) is always a block of zeros. This makes the resulting cipher text much more predictable and susceptible to a dictionary attack.

Potential Mitigations

Phase: Implementation

It is important to properly initialize CBC operating block ciphers or their utility is lost.

Background Details

CBC is the most commonly used mode of operation for a block cipher. It solves electronic code book's dictionary problems by XORing the ciphertext with plaintext. If it used to encrypt multiple data streams, dictionary attacks are possible, provided that the streams have a common beginning sequence.

Relationships

Nature	Type	ID	Name	View(s) this relationship pertains to
ChildOf	Category	310	Cryptographic Issues	Development Concepts (primary)699
ChildOf	Weakness Class	330	Use of Insufficiently Random Values	Research Concepts (primary)1000
ChildOf	Weakness Class	573	Improper Following of Specification by Caller	Research Concepts1000
ChildOf	Category	959	SFP Secondary Cluster: Weak Cryptography	Software Fault Pattern (SFP) Clusters (primary)888

Functional Areas

Cryptography

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
CLASP			Not using a random IV with CBC mode

References

[REF-7] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 2, "Initialization Vectors", Page 42.. 1st Edition. Addison Wesley. 2006.

Content History

Submissions
Submission Date	Submitter	Organization	Source
	CLASP		Externally Mined

Modifications
Modification Date	Modifier	Organization	Source
2008-07-01	Eric Dalci	Cigital	External
2008-07-01	updated Time_of_Introduction
2008-09-08	CWE Content Team	MITRE	Internal
2008-09-08	updated Background_Details, Common_Consequences, Functional_Areas, Relationships, Taxonomy_Mappings
2011-06-01	CWE Content Team	MITRE	Internal
2011-06-01	updated Common_Consequences
2012-05-11	CWE Content Team	MITRE	Internal
2012-05-11	updated References, Relationships
2012-10-30	CWE Content Team	MITRE	Internal
2012-10-30	updated Demonstrative_Examples, Potential_Mitigations
2014-07-30	CWE Content Team	MITRE	Internal
2014-07-30	updated Relationships


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Common Weakness Enumeration

CWE-329: Not Using a Random IV with CBC Mode