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yoffyoff
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Merge pull request #5075 from RasmusWL/crypto
Python: Port py/weak-crypto-key to use type-tracking
2 parents f4dc5b9 + 7b92012 commit 746e994

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‎docs/codeql/support/reusables/frameworks.rst‎

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MySQLdb, Database
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psycopg2, Database
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sqlite3, Database
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cryptography, Cryptography library
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pycryptodome, Cryptography library
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pycryptodomex, Cryptography library

‎python/change-notes/2021-02-02-port-weak-crypto-key-query.md‎

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lgtm,codescanning
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* Updated _Use of weak cryptographic key_ (`py/weak-crypto-key`) query to use the new type-tracking approach instead of points-to analysis. You may see differences in the results found by the query, but overall this change should result in a more robust and accurate analysis.
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* Renamed the query file for _Use of weak cryptographic key_ (`py/weak-crypto-key`) from `WeakCrypto.ql` to `WeakCryptoKey.ql` (in the `python/ql/src/Security/CWE-326/` folder). This will affect any custom query suites that include or exclude this query using its path.

python/ql/src/Security/CWE-326/WeakCrypto.qhelp renamed to python/ql/src/Security/CWE-326/WeakCryptoKey.qhelp

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‎python/ql/src/Security/CWE-326/WeakCryptoKey.ql‎

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/**
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* @name Use of weak cryptographic key
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* @description Use of a cryptographic key that is too small may allow the encryption to be broken.
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* @kind problem
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* @problem.severity error
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* @precision high
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* @id py/weak-crypto-key
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* @tags security
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* external/cwe/cwe-326
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*/
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import python
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import semmle.python.Concepts
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import semmle.python.dataflow.new.DataFlow
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import semmle.python.filters.Tests
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from Cryptography::PublicKey::KeyGeneration keyGen, int keySize, DataFlow::Node origin
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where
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keySize = keyGen.getKeySizeWithOrigin(origin) and
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keySize < keyGen.minimumSecureKeySize() and
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not origin.getScope().getScope*() instanceof TestScope
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select keyGen,
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"Creation of an " + keyGen.getName() + " key uses $@ bits, which is below " +
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keyGen.minimumSecureKeySize() + " and considered breakable.", origin, keySize.toString()

python/ql/src/Security/CWE-326/WeakCrypto.ql renamed to python/ql/src/experimental/Security-old-dataflow/CWE-326/WeakCrypto.ql

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‎python/ql/src/semmle/python/Concepts.qll‎

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@@ -526,3 +526,116 @@ module HTTP {
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}
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}
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}
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/** Provides models for cryptographic things. */
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module Cryptography {
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/** Provides models for public-key cryptography, also called asymmetric cryptography. */
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module PublicKey {
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/**
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* A data-flow node that generates a new key-pair for use with public-key cryptography.
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*
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* Extend this class to refine existing API models. If you want to model new APIs,
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* extend `KeyGeneration::Range` instead.
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*/
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class KeyGeneration extends DataFlow::Node {
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KeyGeneration::Range range;
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KeyGeneration() { this = range }
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/** Gets the name of the cryptographic algorithm (for example `"RSA"` or `"AES"`). */
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string getName() { result = range.getName() }
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/** Gets the argument that specifies the size of the key in bits, if available. */
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DataFlow::Node getKeySizeArg() { result = range.getKeySizeArg() }
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/**
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* Gets the size of the key generated (in bits), as well as the `origin` that
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* explains how we obtained this specific key size.
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*/
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int getKeySizeWithOrigin(DataFlow::Node origin) {
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result = range.getKeySizeWithOrigin(origin)
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}
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/** Gets the minimum key size (in bits) for this algorithm to be considered secure. */
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int minimumSecureKeySize() { result = range.minimumSecureKeySize() }
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}
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/** Provides classes for modeling new key-pair generation APIs. */
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module KeyGeneration {
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/** Gets a back-reference to the keysize argument `arg` that was used to generate a new key-pair. */
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DataFlow::LocalSourceNode keysizeBacktracker(DataFlow::TypeBackTracker t, DataFlow::Node arg) {
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t.start() and
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arg = any(KeyGeneration::Range r).getKeySizeArg() and
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result = arg.getALocalSource()
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or
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// Due to bad performance when using normal setup with we have inlined that code and forced a join
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exists(DataFlow::TypeBackTracker t2 |
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exists(DataFlow::StepSummary summary |
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keysizeBacktracker_first_join(t2, arg, result, summary) and
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t = t2.prepend(summary)
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)
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)
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}
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pragma[nomagic]
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private predicate keysizeBacktracker_first_join(
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DataFlow::TypeBackTracker t2, DataFlow::Node arg, DataFlow::Node res,
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DataFlow::StepSummary summary
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) {
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DataFlow::StepSummary::step(res, keysizeBacktracker(t2, arg), summary)
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}
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/** Gets a back-reference to the keysize argument `arg` that was used to generate a new key-pair. */
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DataFlow::LocalSourceNode keysizeBacktracker(DataFlow::Node arg) {
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result = keysizeBacktracker(DataFlow::TypeBackTracker::end(), arg)
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}
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/**
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* A data-flow node that generates a new key-pair for use with public-key cryptography.
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*
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* Extend this class to model new APIs. If you want to refine existing API models,
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* extend `KeyGeneration` instead.
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*/
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abstract class Range extends DataFlow::Node {
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/** Gets the name of the cryptographic algorithm (for example `"RSA"`). */
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abstract string getName();
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/** Gets the argument that specifies the size of the key in bits, if available. */
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abstract DataFlow::Node getKeySizeArg();
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/**
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* Gets the size of the key generated (in bits), as well as the `origin` that
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* explains how we obtained this specific key size.
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*/
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int getKeySizeWithOrigin(DataFlow::Node origin) {
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origin = keysizeBacktracker(this.getKeySizeArg()) and
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result = origin.asExpr().(IntegerLiteral).getValue()
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}
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/** Gets the minimum key size (in bits) for this algorithm to be considered secure. */
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abstract int minimumSecureKeySize();
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}
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/** A data-flow node that generates a new RSA key-pair. */
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abstract class RsaRange extends Range {
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final override string getName() { result = "RSA" }
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final override int minimumSecureKeySize() { result = 2048 }
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}
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/** A data-flow node that generates a new DSA key-pair. */
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abstract class DsaRange extends Range {
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final override string getName() { result = "DSA" }
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final override int minimumSecureKeySize() { result = 2048 }
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}
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/** A data-flow node that generates a new ECC key-pair. */
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abstract class EccRange extends Range {
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final override string getName() { result = "ECC" }
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final override int minimumSecureKeySize() { result = 224 }
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}
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}
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}
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}

‎python/ql/src/semmle/python/Frameworks.qll‎

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* Helper file that imports all framework modeling.
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*/
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private import semmle.python.frameworks.Cryptodome
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private import semmle.python.frameworks.Cryptography
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private import semmle.python.frameworks.Dill
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private import semmle.python.frameworks.Django
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private import semmle.python.frameworks.Fabric

‎python/ql/src/semmle/python/frameworks/Cryptodome.qll‎

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/**
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* Provides classes modeling security-relevant aspects of
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* - the `pycryptodome` PyPI package (imported as `Crypto`)
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* - the `pycryptodomex` PyPI package (imported as `Cryptodome`)
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* See https://pycryptodome.readthedocs.io/en/latest/.
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*/
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private import python
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private import semmle.python.dataflow.new.DataFlow
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private import semmle.python.Concepts
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private import semmle.python.ApiGraphs
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/**
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* Provides models for
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* - the `pycryptodome` PyPI package (imported as `Crypto`)
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* - the `pycryptodomex` PyPI package (imported as `Cryptodome`)
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* See https://pycryptodome.readthedocs.io/en/latest/
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*/
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private module CryptodomeModel {
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// ---------------------------------------------------------------------------
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/**
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* A call to `Cryptodome.PublicKey.RSA.generate`/`Crypto.PublicKey.RSA.generate`
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*
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* See https://pycryptodome.readthedocs.io/en/latest/src/public_key/rsa.html#Crypto.PublicKey.RSA.generate
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*/
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class CryptodomePublicKeyRsaGenerateCall extends Cryptography::PublicKey::KeyGeneration::RsaRange,
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DataFlow::CallCfgNode {
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CryptodomePublicKeyRsaGenerateCall() {
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this =
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API::moduleImport(["Crypto", "Cryptodome"])
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.getMember("PublicKey")
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.getMember("RSA")
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.getMember("generate")
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.getACall()
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}
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override DataFlow::Node getKeySizeArg() {
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result in [this.getArg(0), this.getArgByName("bits")]
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}
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}
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/**
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* A call to `Cryptodome.PublicKey.DSA.generate`/`Crypto.PublicKey.DSA.generate`
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*
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* See https://pycryptodome.readthedocs.io/en/latest/src/public_key/dsa.html#Crypto.PublicKey.DSA.generate
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*/
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class CryptodomePublicKeyDsaGenerateCall extends Cryptography::PublicKey::KeyGeneration::DsaRange,
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DataFlow::CallCfgNode {
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CryptodomePublicKeyDsaGenerateCall() {
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this =
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API::moduleImport(["Crypto", "Cryptodome"])
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.getMember("PublicKey")
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.getMember("DSA")
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.getMember("generate")
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.getACall()
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}
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override DataFlow::Node getKeySizeArg() {
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result in [this.getArg(0), this.getArgByName("bits")]
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}
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}
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/**
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* A call to `Cryptodome.PublicKey.ECC.generate`/`Crypto.PublicKey.ECC.generate`
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*
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* See https://pycryptodome.readthedocs.io/en/latest/src/public_key/ecc.html#Crypto.PublicKey.ECC.generate
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*/
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class CryptodomePublicKeyEccGenerateCall extends Cryptography::PublicKey::KeyGeneration::EccRange,
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DataFlow::CallCfgNode {
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CryptodomePublicKeyEccGenerateCall() {
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this =
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API::moduleImport(["Crypto", "Cryptodome"])
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.getMember("PublicKey")
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.getMember("ECC")
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.getMember("generate")
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.getACall()
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}
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/** Gets the argument that specifies the curve to use (a string). */
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DataFlow::Node getCurveArg() { result = this.getArgByName("curve") }
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/** Gets the name of the curve to use, as well as the origin that explains how we obtained this name. */
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string getCurveWithOrigin(DataFlow::Node origin) {
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exists(StrConst str | origin = DataFlow::exprNode(str) |
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origin = this.getCurveArg().getALocalSource() and
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result = str.getText()
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)
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}
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override int getKeySizeWithOrigin(DataFlow::Node origin) {
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exists(string curve | curve = this.getCurveWithOrigin(origin) |
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// using list from https://pycryptodome.readthedocs.io/en/latest/src/public_key/ecc.html
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curve in ["NIST P-256", "p256", "P-256", "prime256v1", "secp256r1"] and result = 256
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or
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curve in ["NIST P-384", "p384", "P-384", "prime384v1", "secp384r1"] and result = 384
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or
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curve in ["NIST P-521", "p521", "P-521", "prime521v1", "secp521r1"] and result = 521
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)
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}
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// Note: There is not really a key-size argument, since it's always specified by the curve.
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override DataFlow::Node getKeySizeArg() { none() }
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}
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}

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