pkcs7.go

// This file was written by the tokenizer team at
// https://github.com/go-web/tokenizer and included for use in Quicksilver
// with minor modifications.
//
// =========================================================================
//
// Copyright 2017 tokenizer 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.
//    * The names of authors or contributors may NOT 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,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package crypto

import (
	"bytes"
	"errors"
)

// PKCS7 padding.

// PKCS7 errors.
var (
	// ErrInvalidBlockSize indicates hash blocksize <= 0.
	ErrInvalidBlockSize = errors.New("invalid blocksize")

	// ErrInvalidPKCS7Data indicates bad input to PKCS7 pad or unpad.
	ErrInvalidPKCS7Data = errors.New("invalid PKCS7 data (empty or not padded)")

	// ErrInvalidPKCS7Padding indicates PKCS7 unpad fails to bad input.
	ErrInvalidPKCS7Padding = errors.New("invalid padding on input")
)

// pkcs7Pad right-pads the given byte slice with 1 to n bytes, where
// n is the block size. The size of the result is x times n, where x
// is at least 1.
func PKCS7Pad(b []byte, blocksize int) ([]byte, error) {
	if blocksize <= 0 {
		return nil, ErrInvalidBlockSize
	}
	if b == nil || len(b) == 0 {
		return nil, ErrInvalidPKCS7Data
	}
	n := blocksize - (len(b) % blocksize)
	pb := make([]byte, len(b)+n)
	copy(pb, b)
	copy(pb[len(b):], bytes.Repeat([]byte{byte(n)}, n))
	return pb, nil
}

// pkcs7Unpad validates and unpads data from the given bytes slice.
// The returned value will be 1 to n bytes smaller depending on the
// amount of padding, where n is the block size.
func PKCS7Unpad(b []byte, blocksize int) ([]byte, error) {
	if blocksize <= 0 {
		return nil, ErrInvalidBlockSize
	}
	if b == nil || len(b) == 0 {
		return nil, ErrInvalidPKCS7Data
	}
	if len(b)%blocksize != 0 {
		return nil, ErrInvalidPKCS7Padding
	}
	c := b[len(b)-1]
	n := int(c)
	if n == 0 || n > len(b) {
		return nil, ErrInvalidPKCS7Padding
	}
	for i := 0; i < n; i++ {
		if b[len(b)-n+i] != c {
			return nil, ErrInvalidPKCS7Padding
		}
	}
	return b[:len(b)-n], nil
}