51 lines
1.8 KiB
Plaintext
51 lines
1.8 KiB
Plaintext
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When CBC (Cypher Block Chaining) is used for encryption, the IV (Initialization Vector) must be random an unpredictable. Otherwise it exposes the encrypted value to crypto-analysis attacks like "Chosen-Plaintext Attacks".
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An IV should be used in one and only one encryption cycle because its purpose is to ensure that a different cyphertext value results each time a given plain text value is encrypted.
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== Noncompliant Code Example
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----
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public String cbcEncrypt(String strKey, String plainText) {
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String strIV = "7cVgr5cbdCZVw5WY";
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IvParameterSpec ivSpec = new IvParameterSpec(strIV.getBytes("UTF-8"));
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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, ivSpec); // Noncompliant
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byte[] encryptedBytes = cipher.doFinal(plaintText.getBytes("UTF-8"));
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return DatatypeConverter.printBase64Binary(ivBytes) + ";" + DatatypeConverter.printBase64Binary(encryptedBytes);
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}
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----
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== Compliant Solution
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----
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private SecureRandom random = new SecureRandom();
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public void cbcEncrypt(String strKey, String plainText) {
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byte ivBytes[] = new byte[16];
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random.nextBytes(ivBytes);
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IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
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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, ivSpec);
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byte[] encryptedBytes = cipher.doFinal(plaintText.getBytes("UTF-8"));
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return DatatypeConverter.printBase64Binary(ivBytes) + ";" + DatatypeConverter.printBase64Binary(encryptedBytes);
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}
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----
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== See
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* https://cwe.mitre.org/data/definitions/329.html[MITRE, CWE-329] - Not Using a Random IV with CBC Mode
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* OWASP Top 10 2017 Category A6 - Security Misconfiguration
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