// https://cs.opensource.google/go/go/+/refs/tags/go1.18.3:src/crypto/rsa/rsa.go // Copyright (c) 2009 The Go Authors. All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. package pss import ( "hash" ) // incCounter increments a four byte, big-endian counter. func incCounter(c *[4]byte) { if c[3]++; c[3] != 0 { return } if c[2]++; c[2] != 0 { return } if c[1]++; c[1] != 0 { return } c[0]++ } // mgf1XOR XORs the bytes in out with a mask generated using the MGF1 function // specified in PKCS #1 v2.1. func mgf1XOR(out []byte, hash hash.Hash, seed []byte) { var counter [4]byte var digest []byte done := 0 for done < len(out) { hash.Write(seed) hash.Write(counter[0:4]) digest = hash.Sum(digest[:0]) hash.Reset() for i := 0; i < len(digest) && done < len(out); i++ { out[done] ^= digest[i] done++ } incCounter(&counter) } }