/**
* Find Security Bugs
* Copyright (c) Philippe Arteau, All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3.0 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library.
*/
package com.h3xstream.findsecbugs.crypto;
import com.h3xstream.findsecbugs.common.ByteCode;
import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.Detector;
import edu.umd.cs.findbugs.Priorities;
import edu.umd.cs.findbugs.ba.AnalysisContext;
import edu.umd.cs.findbugs.ba.CFG;
import edu.umd.cs.findbugs.ba.CFGBuilderException;
import edu.umd.cs.findbugs.ba.ClassContext;
import edu.umd.cs.findbugs.ba.DataflowAnalysisException;
import edu.umd.cs.findbugs.ba.Location;
import java.util.Iterator;
import javax.crypto.Cipher;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.ICONST;
import org.apache.bcel.generic.INVOKESPECIAL;
import org.apache.bcel.generic.INVOKEVIRTUAL;
import org.apache.bcel.generic.Instruction;
/**
* <p>
* The main goal of the this detector is to find encryption being done with static initialization vector (IV).
* By design, the IV should be change for every message encrypt by a system.
* </p>
* <h3>Note on the implementation</h3>
* <p>
* The strategy to find those occurrences is not to backtrack to find the potential source of the bytes being passed.
* It will not be trigger if SecureRandom instance is use. Therefor, it is very likely to trigger false positive if the
* encryption is separate from the IV generation.
* </p>
*/
public class StaticIvDetector implements Detector {
private static final boolean DEBUG = false;
private static final String STATIC_IV = "STATIC_IV";
private final BugReporter bugReporter;
public StaticIvDetector(BugReporter bugReporter) {
this.bugReporter = bugReporter;
}
@Override
public void visitClassContext(ClassContext classContext) {
JavaClass javaClass = classContext.getJavaClass();
Method[] methodList = javaClass.getMethods();
for (Method m : methodList) {
try {
analyzeMethod(m, classContext);
} catch (CFGBuilderException | DataflowAnalysisException e) {
AnalysisContext.logError("Cannot analyze method", e);
}
}
}
private void analyzeMethod(Method m, ClassContext classContext) throws CFGBuilderException, DataflowAnalysisException {
ConstantPoolGen cpg = classContext.getConstantPoolGen();
CFG cfg = classContext.getCFG(m);
boolean foundSafeIvGeneration = false;
//Detect if the method is doing decryption only. If it is the case, IV should not be generated from this point
//therefore it is a false positive
boolean atLeastOneDecryptCipher = false;
boolean atLeastOneEncryptCipher = false;
boolean ivFetchFromCipher = false;
//First pass : it look for encryption and decryption mode to detect if the method does decryption only
for (Iterator<Location> i = cfg.locationIterator(); i.hasNext(); ) {
Location location = nextLocation(i, cpg);
Instruction inst = location.getHandle().getInstruction();
//ByteCode.printOpCode(inst,cpg);
if (inst instanceof INVOKEVIRTUAL) {
INVOKEVIRTUAL invoke = (INVOKEVIRTUAL) inst;
//INVOKEVIRTUAL javax/crypto/Cipher.init ((ILjava/security/Key;)V)
if (("javax.crypto.Cipher").equals(invoke.getClassName(cpg)) &&
"init".equals(invoke.getMethodName(cpg))) {
ICONST iconst = ByteCode.getPrevInstruction(location.getHandle(), ICONST.class);
if (iconst != null) {
int mode = iconst.getValue().intValue();
switch (mode) {
case Cipher.ENCRYPT_MODE:
atLeastOneEncryptCipher = true;
break;
case Cipher.DECRYPT_MODE:
atLeastOneDecryptCipher = true;
break;
}
}
}
//INVOKEVIRTUAL javax/crypto/Cipher.getIV (()[B)
else if (("javax.crypto.Cipher").equals(invoke.getClassName(cpg)) &&
"getIV".equals(invoke.getMethodName(cpg))) {
ivFetchFromCipher = true;
}
}
}
//Second pass : It look for encryption method and a potential preceding SecureRandom usage
for (Iterator<Location> i = cfg.locationIterator(); i.hasNext(); ) {
Location location = nextLocation(i, cpg);
Instruction inst = location.getHandle().getInstruction();
if (inst instanceof INVOKEVIRTUAL) {
INVOKEVIRTUAL invoke = (INVOKEVIRTUAL) inst;
if ("java.security.SecureRandom".equals(invoke.getClassName(cpg)) &&
"nextBytes".equals(invoke.getMethodName(cpg))) {
foundSafeIvGeneration = true;
}
} else if (inst instanceof INVOKESPECIAL &&
!ivFetchFromCipher //IV was generate with the KeyGenerator
&& (!atLeastOneDecryptCipher || atLeastOneEncryptCipher) //The cipher is in decrypt mode (no iv generation)
&& !foundSafeIvGeneration) {
INVOKESPECIAL invoke = (INVOKESPECIAL) inst;
if (("javax.crypto.spec.IvParameterSpec").equals(invoke.getClassName(cpg)) &&
"<init>".equals(invoke.getMethodName(cpg))) {
JavaClass clz = classContext.getJavaClass();
bugReporter.reportBug(new BugInstance(this, STATIC_IV, Priorities.NORMAL_PRIORITY) //
.addClass(clz)
.addMethod(clz,m)
.addSourceLine(classContext,m,location));
}
}
}
}
private Location nextLocation(Iterator<Location> i,ConstantPoolGen cpg) {
Location loc = i.next();
if(DEBUG) {
ByteCode.printOpCode(loc.getHandle().getInstruction(), cpg);
}
return loc;
}
@Override
public void report() {
}
}