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pkcs7.go
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pkcs7.go
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/*
* Copyright (C) 2015-2018 Virgil Security Inc.
*
* Lead Maintainer: Virgil Security Inc. <support@virgilsecurity.com>
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* (1) Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* (2) 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.
*
* (3) Neither the name of the copyright holder 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 AUTHOR ''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 AUTHOR 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 cryptoimpl
import (
"bytes"
)
var (
// ErrInvalidBlockSize indicates hash blocksize <= 0.
ErrInvalidBlockSize = CryptoError("invalid blocksize")
// ErrInvalidPKCS7Data indicates bad input to PKCS7 pad or unpad.
ErrInvalidPKCS7Data = CryptoError("invalid PKCS7 data (empty or not padded)")
// ErrInvalidPKCS7Padding indicates PKCS7 unpad fails to bad input.
ErrInvalidPKCS7Padding = CryptoError("invalid padding on input")
)
// 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
}
// 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
}