code: public void setExternalDigest(byte digest[], byte RSAdata[], String digestEncryptionAlgorithm) {
          externalDigest = digest;
          externalRSAdata = RSAdata;
          this.digestEncryptionAlgorithm = digestEncryptionAlgorithm;
      }
docs: Sets the digest/signature to an external calculated value.
  @param digest the digest. This is the actual signature
  @param RSAdata the extra data that goes into the data tag in PKCS#7
  @param digestEncryptionAlgorithm the encryption algorithm. It may must be <CODE>null</CODE> if the <CODE>digest</CODE>
  is also <CODE>null</CODE>. If the <CODE>digest</CODE> is not <CODE>null</CODE>
  then it may be "RSA" or "DSA"