Address review comments

core/src/main/kotlin/com/r3corda/core/transactions/SignedTransaction.kt

@@ -55,8 +55,7 @@ data class SignedTransaction(val txBits: SerializedBytes<WireTransaction>,
     @Throws(SignatureException::class)
     fun verifySignatures(vararg allowedToBeMissing: PublicKey): WireTransaction {
         // Embedded WireTransaction is not deserialised until after we check the signatures.
-        for (sig in sigs)
+        checkSignaturesAreValid()
-            sig.verifyWithECDSA(txBits.bits)
 
         val missing = getMissingSignatures()
         if (missing.isNotEmpty()) {
@@ -68,6 +67,20 @@ data class SignedTransaction(val txBits: SerializedBytes<WireTransaction>,
         return tx
     }
 
+    /**
+     * Mathematically validates the signatures that are present on this transaction. This does not imply that
+     * the signatures are by the right keys, or that there are sufficient signatures, just that they aren't
+     * corrupt. If you use this function directly you'll need to do the other checks yourself. Probably you
+     * want [verifySignatures] instead.
+     *
+     * @throws SignatureException if a signature fails to verify.
+     */
+    @Throws(SignatureException::class)
+    fun checkSignaturesAreValid() {
+        for (sig in sigs)
+            sig.verifyWithECDSA(txBits.bits)
+    }
+
     private fun getMissingSignatures(): Set<PublicKey> {
         val requiredKeys = tx.mustSign.toSet()
         val sigKeys = sigs.map { it.by }.toSet()