CWE-329: Not Using a Random IV with CBC Mode
Not Using a Random IV with CBC Mode
Weakness ID: 329 (Weakness Variant) Status: Draft
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
Common Consequences
Scope Effect Confidentiality
If the CBC is not properly initialized, data that is encrypted can be
compromised and therefore be read.
Integrity
If the CBC is not properly initialized, encrypted data could be
tampered with in transfer.
Accountability
Cryptographic based authentication systems could be defeated.
Likelihood of Exploit
Demonstrative Examples
Example 1
(Bad Code)
C and C++
#include <openssl/evp.h> 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)
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);
}
}
Potential Mitigations
Phase Description Integrity: 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
Functional Areas
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name CLASP Not using a random IV with CBC mode
Content History
Submissions Submission Date Submitter Organization Source CLASP Externally Mined Modifications Modification Date Modifier Organization Source 2008-07-01 Eric Dalci Cigital External updated Time of Introduction 2008-09-08 CWE Content Team MITRE Internal updated Background Details, Common Consequences,
Functional Areas, Relationships, Taxonomy Mappings
Description
