add model for the core OpenSSL::Digest module

ruby/ql/lib/codeql/ruby/ApiGraphs.qll

@@ -203,7 +203,7 @@ module API {
     /**
      * Gets a node representing a call to `method` on the receiver represented by this node.
      */
-    Node getMethod(string method) {
+    MethodAccessNode getMethod(string method) {
       result = this.getASubclass().getASuccessor(Label::method(method))
     }
 

ruby/ql/lib/codeql/ruby/security/OpenSSL.qll

@@ -581,3 +581,49 @@ private class CipherOperation extends Cryptography::CryptographicOperation::Rang
     result = cipherNode.getCipherMode().getBlockMode()
   }
 }
+
+/** Predicates and classes modelling the `OpenSSL::Digest` module */
+private module Digest {
+  private import codeql.ruby.ApiGraphs
+
+  /** A call that hashes some input using a hashing algorithm from the `OpenSSL::Digest` module. */
+  private class DigestCall extends Cryptography::CryptographicOperation::Range instanceof DataFlow::CallNode {
+    Cryptography::HashingAlgorithm algo;
+
+    DigestCall() {
+      exists(API::MethodAccessNode call |
+        call = API::getTopLevelMember("OpenSSL").getMember("Digest").getMethod("new")
+      |
+        this = call.getReturn().getAMethodCall(["digest", "update", "<<"]) and
+        algo.matchesName(call.getCallNode()
+              .getArgument(0)
+              .asExpr()
+              .getExpr()
+              .getConstantValue()
+              .getString())
+      )
+    }
+
+    override Cryptography::HashingAlgorithm getAlgorithm() { result = algo }
+
+    override DataFlow::Node getAnInput() { result = super.getArgument(0) }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
+  }
+
+  /** A call to `OpenSSL::Digest.digest` that hashes input directly without constructing a digest instance. */
+  private class DigestCallDirect extends Cryptography::CryptographicOperation::Range instanceof DataFlow::CallNode {
+    Cryptography::HashingAlgorithm algo;
+
+    DigestCallDirect() {
+      this = API::getTopLevelMember("OpenSSL").getMember("Digest").getMethod("digest").getCallNode() and
+      algo.matchesName(this.getArgument(0).asExpr().getExpr().getConstantValue().getString())
+    }
+
+    override Cryptography::HashingAlgorithm getAlgorithm() { result = algo }
+
+    override DataFlow::Node getAnInput() { result = super.getArgument(1) }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
+  }
+}

ruby/ql/test/query-tests/security/cwe-327/BrokenCryptoAlgorithm.expected

@@ -24,3 +24,6 @@
 | broken_crypto.rb:90:1:90:17 | ... << ... | The cryptographic algorithm MD5 is broken or weak, and should not be used. |
 | broken_crypto.rb:95:1:95:34 | call to bubblebabble | The cryptographic algorithm MD5 is broken or weak, and should not be used. |
 | broken_crypto.rb:97:11:97:37 | call to file | The cryptographic algorithm MD5 is broken or weak, and should not be used. |
+| broken_crypto.rb:103:1:103:21 | call to digest | The cryptographic algorithm SHA1 is broken or weak, and should not be used. |
+| broken_crypto.rb:104:1:104:17 | ... << ... | The cryptographic algorithm SHA1 is broken or weak, and should not be used. |
+| broken_crypto.rb:106:1:106:37 | call to digest | The cryptographic algorithm SHA1 is broken or weak, and should not be used. |

ruby/ql/test/query-tests/security/cwe-327/broken_crypto.rb

@@ -97,4 +97,11 @@ Digest::MD5.bubblebabble 'message' # BAD: weak hash algorithm
 filemd5 = Digest::MD5.file 'testfile'
 filemd5.hexdigest
 
-Digest("MD5").hexdigest('foo') # BAD: weak hash algorithm
+Digest("MD5").hexdigest('foo') # BAD: weak hash algorithm
+
+sha1 = OpenSSL::Digest.new('SHA1')
+sha1.digest 'message' # BAD: weak hash algorithm
+sha1 << 'message' # << is an alias for update
+
+OpenSSL::Digest.digest('SHA1', "abc") # BAD: weak hash algorithm
+OpenSSL::Digest.digest('SHA3-512', "abc") # GOOD: strong hash algorithm