Improve qhelp for broken crypto algo queries

Previously it focussed too much on the risk of data being decrypted,
and didn't explain why using weak algorithms is a problem in other
contexts.

javascript/ql/src/Security/CWE-327/BrokenCryptoAlgorithm.qhelp

@@ -4,17 +4,34 @@
 <qhelp>
 	<overview>
 		<p>
-			Using broken or weak cryptographic algorithms can leave data
-			vulnerable to being decrypted or forged by an attacker.
+			Using broken or weak cryptographic algorithms may compromise
+			security guarantees such as confidentiality, integrity, and
+			authenticity.
 		</p>
 
 		<p>
-			Many cryptographic algorithms provided by cryptography
-			libraries are known to be weak, or flawed. Using such an
-			algorithm means that encrypted or hashed data is less
-			secure than it appears to be.
+			Many cryptographic algorithms are known to be weak or flawed. The
+			security guarantees of a system often rely on the underlying
+			cryptography, so using a weak algorithm can have severe consequences.
+			For example:
 		</p>
 
+		<ul>
+			<li>
+			If a weak encryption algorithm is used, an attacker may be able to
+			decrypt sensitive data.
+			</li>
+			<li>
+			If a weak hashing algorithm is used to protect data integrity, an
+			attacker may be able to craft a malicious input that has the same
+			hash as a benign one.
+			</li>
+			<li>
+			If a weak algorithm is used for digital signatures, an attacker may
+			be able to forge signatures and impersonate legitimate users.
+			</li>
+		</ul>
+
 	</overview>
 	<recommendation>