Ensure primary key meets strength and algo requirements when encrypting/verifying/signing using subkeys (#1719)

Breaking change: the requirements of `config.minRSABits`, `rejectPublicKeyAlgorithms` and `rejectCurves`
are now applied to the primary key, aside from the selected subkey.

The motivation is that the subkeys are certified by the primary key, but if the latter is
weak, arbitrary subkeys could potentially be added.

Note that the change does not affect decryption, to allow decrypting older messages.

src/key/key.js

@@ -259,6 +259,11 @@ class Key {
   async getSigningKey(keyID = null, date = new Date(), userID = {}, config = defaultConfig) {
     await this.verifyPrimaryKey(date, userID, config);
     const primaryKey = this.keyPacket;
+    try {
+      helper.checkKeyRequirements(primaryKey, config);
+    } catch (err) {
+      throw util.wrapError('Could not verify primary key', err);
+    }
     const subkeys = this.subkeys.slice().sort((a, b) => b.keyPacket.created - a.keyPacket.created);
     let exception;
     for (const subkey of subkeys) {
@@ -313,6 +318,11 @@ class Key {
   async getEncryptionKey(keyID, date = new Date(), userID = {}, config = defaultConfig) {
     await this.verifyPrimaryKey(date, userID, config);
     const primaryKey = this.keyPacket;
+    try {
+      helper.checkKeyRequirements(primaryKey, config);
+    } catch (err) {
+      throw util.wrapError('Could not verify primary key', err);
+    }
     // V4: by convention subkeys are preferred for encryption service
     const subkeys = this.subkeys.slice().sort((a, b) => b.keyPacket.created - a.keyPacket.created);
     let exception;

test/general/config.js

@@ -300,10 +300,25 @@ n9/quqtmyOtYOA6gXNCw0Fal3iANKBmsPmYI
         message, encryptionKeys: [key], config: { rejectCurves: new Set([openpgp.enums.curve.curve25519Legacy]) }
       })).to.be.eventually.rejectedWith(/Support for ecdh keys using curve curve25519Legacy is disabled/);
 
-      const echdEncrypted = await openpgp.encrypt({
+      await expect(openpgp.encrypt({
         message, encryptionKeys: [key], config: { rejectCurves: new Set([openpgp.enums.curve.ed25519Legacy]) }
-      });
-      expect(echdEncrypted).to.match(/---BEGIN PGP MESSAGE---/);
+      })).to.be.eventually.rejectedWith(/Could not verify primary key: Support for eddsaLegacy keys using curve ed25519Legacy is disabled/);
+
+      // RSA 512 bits primary key, ECC subkey
+      const weakPrimaryKey = await openpgp.readKey({ armoredKey: `-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+-----END PGP PUBLIC KEY BLOCK-----` });
+      await expect(openpgp.encrypt({ message, encryptionKeys: weakPrimaryKey, config: { minRSABits: 2048 } })).to.be.rejectedWith(/Could not verify primary key: RSA keys shorter than 2048 bits are considered too weak./);
     } finally {
       openpgp.config.aeadProtect = aeadProtectVal;
       openpgp.config.preferredCompressionAlgorithm = preferredCompressionAlgorithmVal;

test/general/key.js

@@ -4284,11 +4284,9 @@ VYGdb3eNlV8CfoEC
 
   it('Reject encryption with key revoked with appended revocation cert', async function() {
     const key = await openpgp.readKey({ armoredKey: pub_revoked_with_cert });
-    return openpgp.encrypt({ encryptionKeys: [key], message: await openpgp.createMessage({ text: 'random data' }) }).then(() => {
-      throw new Error('encryptSessionKey should not encrypt with revoked public key');
-    }).catch(function(error) {
-      expect(error.message).to.equal('Error encrypting message: Primary key is revoked');
-    });
+    await expect(
+      openpgp.encrypt({ encryptionKeys: [key], message: await openpgp.createMessage({ text: 'random data' }) })
+    ).to.be.rejectedWith(/Primary key is revoked/);
   });
 
   it('Merge key with another key with non-ID user attributes', async function() {

test/general/openpgp.js

@@ -3990,7 +3990,7 @@ XfA3pqV4mTzF
           }).then(function() {
             throw new Error('Should not encrypt with revoked key');
           }).catch(function(error) {
-            expect(error.message).to.match(/Error encrypting message: Primary key is revoked/);
+            expect(error.message).to.match(/Primary key is revoked/);
           });
         });
       });

test/general/signature.js

@@ -895,7 +895,8 @@ DQmhI0SZoTKy4EGhS0bNJ+g2+dJ8Y22fKzLWXwo=
     await expect(openpgp.sign({
       signingKeys: key,
       date: new Date(key.keyPacket.created - 3600),
-      message: await openpgp.createMessage({ text: 'Hello World' })
+      message: await openpgp.createMessage({ text: 'Hello World' }),
+      config: { minRSABits: 1024 }
     })).to.be.rejectedWith(/Signature creation time is in the future/);
   });