padding.go

// From https://github.com/go-web/tokenizer/blob/master/pkcs7.go

// 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,
// 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 sfgo

import (
	"bytes"
	"errors"
)

// 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, errors.New("ErrInvalidBlockSize")
	}
	if b == nil || len(b) == 0 {
		return nil, errors.New("ErrInvalidBlockSize")
	}
	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, errors.New("ErrInvalidBlockSize")
	}
	if b == nil || len(b) == 0 {
		return nil, errors.New("ErrInvalidPKCS7Data")
	}
	if len(b)%blocksize != 0 {
		return nil, errors.New("ErrInvalidPKCS7Padding")
	}
	c := b[len(b)-1]
	n := int(c)
	if n == 0 || n > len(b) {
		return nil, errors.New("ErrInvalidPKCS7Padding")
	}
	for i := 0; i < n; i++ {
		if b[len(b)-n+i] != c {
			return nil, errors.New("ErrInvalidPKCS7Padding")
		}
	}
	return b[:len(b)-n], nil
}