61 lines
1.5 KiB
Go
61 lines
1.5 KiB
Go
package nametransform
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import (
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"crypto/aes"
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"errors"
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"fmt"
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)
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// pad16 - pad data to AES block size (=16 byte) using standard PKCS#7 padding
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// https://tools.ietf.org/html/rfc5652#section-6.3
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func pad16(orig []byte) (padded []byte) {
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oldLen := len(orig)
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if oldLen == 0 {
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panic("Padding zero-length string makes no sense")
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}
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padLen := aes.BlockSize - oldLen%aes.BlockSize
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if padLen == 0 {
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padLen = aes.BlockSize
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}
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newLen := oldLen + padLen
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padded = make([]byte, newLen)
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copy(padded, orig)
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padByte := byte(padLen)
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for i := oldLen; i < newLen; i++ {
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padded[i] = padByte
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}
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return padded
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}
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// unPad16 - remove padding
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func unPad16(padded []byte) ([]byte, error) {
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oldLen := len(padded)
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if oldLen%aes.BlockSize != 0 {
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return nil, errors.New("Unaligned size")
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}
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// The last byte is always a padding byte
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padByte := padded[oldLen-1]
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// The padding byte's value is the padding length
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padLen := int(padByte)
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// Padding must be at least 1 byte
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if padLen <= 0 {
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return nil, errors.New("Padding cannot be zero-length")
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}
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// Larger paddings make no sense
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if padLen > aes.BlockSize {
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return nil, fmt.Errorf("Padding too long, padLen = %d > 16", padLen)
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}
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// All padding bytes must be identical
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for i := oldLen - padLen; i < oldLen; i++ {
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if padded[i] != padByte {
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return nil, fmt.Errorf("Padding byte at i=%d is invalid", i)
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}
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}
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newLen := oldLen - padLen
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// Padding an empty string makes no sense
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if newLen == 0 {
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return nil, errors.New("Unpadded length is zero")
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}
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return padded[0:newLen], nil
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}
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