PKCS#7: Custom message digest

lib/pkcs7.js

@@ -444,44 +444,42 @@ p7.createSignedData = function() {
   }
 
   function addSignerInfos(mds) {
-    var content;
+    var content,
+        bytes;
 
-    if (msg.detachedContent) {
-      // Signature has been made in detached mode.
-      content = msg.detachedContent;
-    } else {
-      // Note: ContentInfo is a SEQUENCE with 2 values, second value is
-      // the content field and is optional for a ContentInfo but required here
-      // since signers are present
-      // get ContentInfo content
-      content = msg.contentInfo.value[1];
-      // skip [0] EXPLICIT content wrapper
-      content = content.value[0];
-    }
+    if (msg.content) {
+      if (msg.detachedContent) {
+        // Signature has been made in detached mode.
+        content = msg.detachedContent;
+      } else {
+        // Note: ContentInfo is a SEQUENCE with 2 values, second value is
+        // the content field and is optional for a ContentInfo but required here
+        // since signers are present
+        // get ContentInfo content
+        content = msg.contentInfo.value[1];
+        // skip [0] EXPLICIT content wrapper
+        content = content.value[0];
+      }
 
-    if(!content) {
-      throw new Error(
-        'Could not sign PKCS#7 message; there is no content to sign.');
+      // serialize content
+      bytes = asn1.toDer(content);
+
+      // skip identifier and length per RFC 2315 9.3
+      // skip identifier (1 byte)
+      bytes.getByte();
+      // read and discard length bytes
+      asn1.getBerValueLength(bytes);
+      bytes = bytes.getBytes();
+
+      // digest content DER value bytes
+      for(var oid in mds) {
+        mds[oid].start().update(bytes);
+      }
     }
 
     // get ContentInfo content type
     var contentType = asn1.derToOid(msg.contentInfo.value[0].value);
 
-    // serialize content
-    var bytes = asn1.toDer(content);
-
-    // skip identifier and length per RFC 2315 9.3
-    // skip identifier (1 byte)
-    bytes.getByte();
-    // read and discard length bytes
-    asn1.getBerValueLength(bytes);
-    bytes = bytes.getBytes();
-
-    // digest content DER value bytes
-    for(var oid in mds) {
-      mds[oid].start().update(bytes);
-    }
-
     // sign content
     var signingTime = new Date();
     for(var i = 0; i < msg.signers.length; ++i) {
@@ -509,8 +507,15 @@ p7.createSignedData = function() {
         for(var ai = 0; ai < signer.authenticatedAttributes.length; ++ai) {
           var attr = signer.authenticatedAttributes[ai];
           if(attr.type === forge.pki.oids.messageDigest) {
-            // use content message digest as value
-            attr.value = mds[signer.digestAlgorithm].digest();
+            // use content message digest as value if not already set
+            if(!attr.value){
+              if(!content) {
+                throw new Error(
+                  'Could not sign PKCS#7 message; there is no content to ' +
+                  'sign or message-digest attribute missing.');
+              }
+              attr.value = mds[signer.digestAlgorithm].digest();
+            }
           } else if(attr.type === forge.pki.oids.signingTime) {
             // auto-populate signing time if not already set
             if(!attr.value) {

tests/unit/pkcs7.js

@@ -4,6 +4,7 @@ var PKCS7 = require('../../lib/pkcs7');
 var PKI = require('../../lib/pki');
 var AES = require('../../lib/aes');
 var DES = require('../../lib/des');
+var SHA256 = require('../../lib/sha256');
 var UTIL = require('../../lib/util');
 
 (function() {
@@ -788,5 +789,33 @@ var UTIL = require('../../lib/util');
       ASSERT.equal(pem, _pem.signedDataWithAttrs1949GeneralizedTime);
     });
 
+    it('should create PKCS#7 SignedData with custom message-digest',
+      function() {
+      var p7 = PKCS7.createSignedData();
+      var messageDigest = SHA256.create().update('To be signed.', 'utf8').digest();
+
+      p7.addCertificate(_pem.certificate);
+      p7.addSigner({
+        key: PKI.privateKeyFromPem(_pem.privateKey),
+        certificate: _pem.certificate,
+        digestAlgorithm: PKI.oids.sha256,
+        authenticatedAttributes: [{
+          type: forge.pki.oids.contentType,
+          value: forge.pki.oids.data
+        }, {
+          type: forge.pki.oids.messageDigest,
+          value: messageDigest
+        }, {
+          type: forge.pki.oids.signingTime,
+          // will be encoded as UTC time because it's >= 1950
+          value: new Date('1950-01-01T00:00:00Z')
+        }]
+      });
+      p7.sign({detached: true});
+
+      var pem = PKCS7.messageToPem(p7);
+      ASSERT.equal(pem, _pem.detachedSignature);
+    });
+
   });
 })();