67 lines
2.5 KiB
Plaintext
67 lines
2.5 KiB
Plaintext
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In encryption, when Cipher Block Chaining (CBC) is used, the Initialization Vector (IV) must be random and unpredictable. Otherwise, the encrypted value is vulnerable to crypto-analysis attacks such as the "Chosen-Plaintext Attack".
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An IV value should be associated to one, and only one encryption cycle, because the IV's purpose is to ensure that the same plaintext encrypted twice will yield two different ciphertexts.
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To that end, IV's should be:
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* random
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* unpredictable
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* publishable (IVs are frequently published)
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* authenticated, along with the ciphertext, with a Message Authentication Code (MAC)
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This rule raises an issue when the IV is:
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* hard-coded
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* created using <code>java.util.Random</code> rather than <code>java.security.SecureRandom</code>.
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== Noncompliant Code Example
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----
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public class MyCbcClass {
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public String applyCBC(String strKey, String plainText) {
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byte[] bytesIV = "7cVgr5cbdCZVw5WY".getBytes("UTF-8");
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/* KEY + IV setting */
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IvParameterSpec iv = new IvParameterSpec(bytesIV);
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SecretKeySpec skeySpec = new SecretKeySpec(strKey.getBytes("UTF-8"), "AES");
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/* Ciphering */
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Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
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cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv); // Noncompliant because IV hard coded and cannot vary with each ciphering round
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byte[] encryptedBytes = cipher.doFinal(plainText.getBytes("UTF-8"));
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return DatatypeConverter.printBase64Binary(bytesIV) // IV is typically published
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+ ";" + DatatypeConverter.printBase64Binary(encryptedBytes);
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}
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}
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----
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== Compliant Solution
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----
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public class MyCbcClass {
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SecureRandom random = new SecureRandom();
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public String applyCBC(String strKey, String plainText) {
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byte[] bytesIV = new byte[16];
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random.nextBytes(bytesIV);
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/* KEY + IV setting */
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IvParameterSpec iv = new IvParameterSpec(bytesIV);
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SecretKeySpec skeySpec = new SecretKeySpec(strKey.getBytes("UTF-8"), "AES");
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/* Ciphering */
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Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
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cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv);
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byte[] encryptedBytes = cipher.doFinal(plainText.getBytes("UTF-8"));
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return DatatypeConverter.printBase64Binary(bytesIV)
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+ ";" + DatatypeConverter.printBase64Binary(encryptedBytes);
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}
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}
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----
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== See
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* http://cwe.mitre.org/data/definitions/330[MITRE, CWE-330] - Use of Insufficiently Random Values
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* OWASP Top 10 2017 Category A6 - Security Misconfiguration
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* Derived from FindSecBugs rule https://find-sec-bugs.github.io/bugs.htm#STATIC_IV[STATIC_IV]
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