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artem-smotrakovartem-smotrakov
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Better docs for java/non-constant-time-crypto-comparison
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Lines changed: 22 additions & 6 deletions

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‎java/ql/src/experimental/Security/CWE/CWE-208/NonConstantTimeCryptoComparison.qhelp‎

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@@ -5,8 +5,8 @@
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<p>
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When comparing results of cryptographic operations, such as MAC or digital signature,
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a constant time algorithm should be used. In other words, the comparison time should not depend on
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the content of the input. Otherwise, an attacker may be able to implement a timing attack.
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A successful timing attack may result in leaking secrets or authentication bypass.
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the content of the input. Otherwise, attackers may be able to implement a timing attack
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if they can control input. A successful timing attack may result in leaking secrets or authentication bypass.
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</p>
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</overview>
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‎java/ql/src/experimental/Security/CWE/CWE-208/NonConstantTimeCryptoComparison.ql‎

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@@ -1,7 +1,7 @@
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/**
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* @name Using a non-constant time algorithm for comparing results of a cryptographic operation
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* @description When comparing results of a cryptographic operation, a constant time algorithm should be used.
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* Otherwise, an attacker may be able to implement a timing attack.
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* Otherwise, attackers may be able to implement a timing attack if they can control input.
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* A successful attack may result in leaking secrets or authentication bypass.
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* @kind path-problem
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* @problem.severity warning
@@ -21,12 +21,15 @@ private class ByteBuffer extends Class {
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ByteBuffer() { hasQualifiedName("java.nio", "ByteBuffer") }
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}
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/** A method call that produces cryptographic result. */
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abstract private class ProduceCryptoCall extends MethodAccess {
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Expr output;
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/** Return the result of cryptographic operation. */
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Expr output() { result = output }
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}
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/** A method call that produces a MAC. */
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private class ProduceMacCall extends ProduceCryptoCall {
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ProduceMacCall() {
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getMethod().hasQualifiedName("javax.crypto", "Mac", "doFinal") and
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}
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}
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/** A method call that produces a signature. */
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private class ProduceSignatureCall extends ProduceCryptoCall {
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ProduceSignatureCall() {
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getMethod().hasQualifiedName("java.security", "Signature", "sign") and
@@ -49,6 +53,7 @@ private class ProduceSignatureCall extends ProduceCryptoCall {
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}
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}
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/** A method call that produces a ciphertext. */
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private class ProduceCiphertextCall extends ProduceCryptoCall {
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ProduceCiphertextCall() {
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getMethod().hasQualifiedName("javax.crypto", "Cipher", "doFinal") and
@@ -63,6 +68,10 @@ private class ProduceCiphertextCall extends ProduceCryptoCall {
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}
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}
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/**
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* A config that tracks data flow from remote user input to a cryptographic operation
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* such as cipher, MAC or signature.
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*/
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private class UserInputInCryptoOperationConfig extends TaintTracking2::Configuration {
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UserInputInCryptoOperationConfig() { this = "UserInputInCryptoOperationConfig" }
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@@ -72,6 +81,7 @@ private class UserInputInCryptoOperationConfig extends TaintTracking2::Configura
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exists(ProduceCryptoCall call | call.getQualifier() = sink.asExpr())
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}
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/** Holds if `fromNode` to `toNode` is a dataflow step that updates a cryptographic operation. */
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override predicate isAdditionalTaintStep(DataFlow2::Node fromNode, DataFlow2::Node toNode) {
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exists(MethodAccess call, Method m |
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m = call.getMethod() and
@@ -90,6 +100,7 @@ private class UserInputInCryptoOperationConfig extends TaintTracking2::Configura
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}
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}
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/** A source that produces result of cryptographic operation. */
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private class CryptoOperationSource extends DataFlow::Node {
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Expr cryptoOperation;
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@@ -99,6 +110,7 @@ private class CryptoOperationSource extends DataFlow::Node {
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)
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}
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/** Holds if remote user input was used in the cryptographic operation. */
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predicate includesUserInput() {
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exists(
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DataFlow2::PathNode source, DataFlow2::PathNode sink, UserInputInCryptoOperationConfig config
@@ -128,6 +140,10 @@ private class NonConstantTimeComparisonCall extends StaticMethodAccess {
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}
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}
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/**
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* A config that tracks data flow from remote user input to methods
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* that compare inputs using a non-constant time algorithm.
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*/
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private class UserInputInComparisonConfig extends TaintTracking2::Configuration {
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UserInputInComparisonConfig() { this = "UserInputInComparisonConfig" }
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}
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}
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/** Holds if `expr` looks like a constant. */
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private predicate looksLikeConstant(Expr expr) {
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expr.isCompileTimeConstant()
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or
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expr.(VarAccess).getVariable().isFinal() and expr.getType() instanceof TypeString
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}
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/**
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* A sink that compares input using a non-constant time algorithm.
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*/
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/** A sink that compares input using a non-constant time algorithm. */
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private class NonConstantTimeComparisonSink extends DataFlow::Node {
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Expr anotherParameter;
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not looksLikeConstant(anotherParameter)
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}
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/** Holds if remote user input was used in the comparison. */
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predicate includesUserInput() {
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exists(UserInputInComparisonConfig config |
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config.hasFlowTo(DataFlow2::exprNode(anotherParameter))

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