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Python: Weak crypto query.
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‎python/ql/src/Security/CWE-326/WeakCrypto.qhelp‎

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

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/**
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* @name Weak Cryptographic Key Use
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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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int minimumSecureKeySize(string algo) {
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algo = "DSA" and result = 2048
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or
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algo = "RSA" and result = 2048
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or
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algo = "elliptic curve" and result = 224
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}
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predicate dsaRsaKeySizeArg(FunctionObject obj, string algorithm, string arg) {
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exists(ModuleObject mod |
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mod.getAttribute(_) = obj |
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algorithm = "DSA" and
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(
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mod.getName() = "cryptography.hazmat.primitives.asymmetric.dsa" and arg = "key_size"
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or
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mod.getName() = "Crypto.PublicKey.DSA" and arg = "bits"
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or
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mod.getName() = "Cryptodome.PublicKey.DSA" and arg = "bits"
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)
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or
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algorithm = "RSA" and
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(
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mod.getName() = "cryptography.hazmat.primitives.asymmetric.rsa" and arg = "key_size"
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or
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mod.getName() = "Crypto.PublicKey.RSA" and arg = "bits"
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or
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mod.getName() = "Cryptodome.PublicKey.RSA" and arg = "bits"
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)
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or
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algorithm = "elliptic curve" and
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mod.getName() = "cryptography.hazmat.primitives.asymmetric.ec" and arg = "curve"
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)
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}
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predicate ecKeySizeArg(FunctionObject obj, string arg) {
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exists(ModuleObject mod |
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mod.getAttribute(_) = obj |
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mod.getName() = "cryptography.hazmat.primitives.asymmetric.ec" and arg = "curve"
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)
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}
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int keySizeFromCurve(ClassObject curveClass) {
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result = curveClass.declaredAttribute("key_size").(NumericObject).intValue()
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}
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predicate algorithmAndKeysizeForCall(CallNode call, string algorithm, int keySize, ControlFlowNode keyOrigin) {
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exists(FunctionObject func, string argname, ControlFlowNode arg |
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arg = func.getNamedArgumentForCall(call, argname) |
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exists(NumericObject key |
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arg.refersTo(key, keyOrigin) and
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dsaRsaKeySizeArg(func, algorithm, argname) and
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keySize = key.intValue()
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)
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or
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exists(ClassObject curve |
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arg.refersTo(_, curve, keyOrigin) and
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ecKeySizeArg(func, argname) and
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algorithm = "elliptic curve" and
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keySize = keySizeFromCurve(curve)
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)
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)
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}
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from CallNode call, ControlFlowNode origin, string algo, int keySize
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where
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algorithmAndKeysizeForCall(call, algo, keySize, origin) and
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keySize < minimumSecureKeySize(algo)
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select call, "Creation of an " + algo + " key uses $@ bits, which is below " + minimumSecureKeySize(algo) + " and considered breakable.", origin, keySize.toString()
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‎python/ql/test/query-tests/Security/CWE-326/WeakCrypto.expected‎

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| weak_crypto.py:67:1:67:30 | ControlFlowNode for dsa_gen_key() | Creation of an DSA key uses $@ bits, which is below 2048 and considered breakable. | weak_crypto.py:12:12:12:15 | ControlFlowNode for IntegerLiteral | 1024 |
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| weak_crypto.py:68:1:68:28 | ControlFlowNode for ec_gen_key() | Creation of an elliptic curve key uses $@ bits, which is below 224 and considered breakable. | weak_crypto.py:21:11:21:33 | ControlFlowNode for FakeWeakEllipticCurve() | 160 |
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| weak_crypto.py:69:1:69:37 | ControlFlowNode for rsa_gen_key() | Creation of an RSA key uses $@ bits, which is below 2048 and considered breakable. | weak_crypto.py:12:12:12:15 | ControlFlowNode for IntegerLiteral | 1024 |
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| weak_crypto.py:71:1:71:22 | ControlFlowNode for Attribute() | Creation of an DSA key uses $@ bits, which is below 2048 and considered breakable. | weak_crypto.py:12:12:12:15 | ControlFlowNode for IntegerLiteral | 1024 |
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| weak_crypto.py:72:1:72:22 | ControlFlowNode for Attribute() | Creation of an RSA key uses $@ bits, which is below 2048 and considered breakable. | weak_crypto.py:12:12:12:15 | ControlFlowNode for IntegerLiteral | 1024 |

‎python/ql/test/query-tests/Security/CWE-326/WeakCrypto.qlref‎

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Security/CWE-326/WeakCrypto.ql

‎python/ql/test/query-tests/Security/CWE-326/options‎

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semmle-extractor-options: -p ../lib/ --max-import-depth=3
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optimize: true

‎python/ql/test/query-tests/Security/CWE-326/weak_crypto.py‎

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from cryptography.hazmat import backends
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from cryptography.hazmat.primitives.asymmetric import ec, dsa, rsa
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#Crypto and Cryptodome have same API
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if random():
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from Crypto.PublicKey import DSA
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from Crypto.PublicKey import RSA
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else:
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from Cryptodome.PublicKey import DSA
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from Cryptodome.PublicKey import RSA
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RSA_WEAK = 1024
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RSA_OK = 2048
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RSA_STRONG = 3076
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BIG = 10000
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class FakeWeakEllipticCurve:
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name = "fake"
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key_size = 160
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EC_WEAK = FakeWeakEllipticCurve()
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EC_OK = ec.SECP224R1()
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EC_STRONG = ec.SECP384R1()
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EC_BIG = ec.SECT571R1()
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dsa_gen_key = dsa.generate_private_key
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ec_gen_key = ec.generate_private_key
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rsa_gen_key = rsa.generate_private_key
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default = backends.default_backend()
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#Strong and OK keys.
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dsa_gen_key(key_size=RSA_OK, backend=default)
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dsa_gen_key(key_size=RSA_STRONG, backend=default)
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dsa_gen_key(key_size=BIG, backend=default)
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ec_gen_key(key_size=EC_OK, backend=default)
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ec_gen_key(key_size=EC_STRONG, backend=default)
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ec_gen_key(key_size=EC_BIG, backend=default)
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rsa_gen_key(public_exponent=65537, key_size=RSA_OK, backend=default)
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rsa_gen_key(public_exponent=65537, key_size=RSA_STRONG, backend=default)
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rsa_gen_key(public_exponent=65537, key_size=BIG, backend=default)
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DSA.generate(bits=RSA_OK)
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DSA.generate(bits=RSA_STRONG)
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RSA.generate(bits=RSA_OK)
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RSA.generate(bits=RSA_STRONG)
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dsa_gen_key(RSA_OK, default)
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dsa_gen_key(RSA_STRONG, default)
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dsa_gen_key(BIG, default)
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ec_gen_key(EC_OK, default)
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ec_gen_key(EC_STRONG, default)
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ec_gen_key(EC_BIG, default)
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rsa_gen_key(65537, RSA_OK, default)
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rsa_gen_key(65537, RSA_STRONG, default)
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rsa_gen_key(65537, BIG, default)
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DSA.generate(RSA_OK)
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DSA.generate(RSA_STRONG)
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RSA.generate(RSA_OK)
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RSA.generate(RSA_STRONG)
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# Weak keys
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dsa_gen_key(RSA_WEAK, default)
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ec_gen_key(EC_WEAK, default)
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rsa_gen_key(65537, RSA_WEAK, default)
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DSA.generate(RSA_WEAK)
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RSA.generate(RSA_WEAK)
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‎python/ql/test/query-tests/Security/lib/Crypto/PublicKey/DSA.py‎

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def generate(bits):
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pass

‎python/ql/test/query-tests/Security/lib/Crypto/PublicKey/RSA.py‎

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def generate(bits):
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pass

‎python/ql/test/query-tests/Security/lib/Crypto/PublicKey/__init__.py‎

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‎python/ql/test/query-tests/Security/lib/cryptography/hazmat/primitives/asymmetric/__init__.py‎

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