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pkcs7.go
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pkcs7.go
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package util
import (
"bytes"
"errors"
)
const pkcs7BlockSize = 32
var (
ErrInvalidBlockSize = errors.New("invalid block size")
ErrInvalidPKCS7Data = errors.New("invalid PKCS7 data")
ErrInvalidPKCS7Padding = errors.New("invalid padding on input")
)
// pkcs7encode 对需要加密的明文进行填充补位
// plaintext 需要进行填充补位操作的明文
// 返回补齐明文字符串
func pkcs7encode(plaintext []byte) []byte {
//计算需要填充的位数
pad := pkcs7BlockSize - len(plaintext)%pkcs7BlockSize
if pad == 0 {
pad = pkcs7BlockSize
}
//获得补位所用的字符
text := bytes.Repeat([]byte{byte(pad)}, pad)
return append(plaintext, text...)
}
// pkcs7decode 对解密后的明文进行补位删除
// plaintext 解密后的明文
// 返回删除填充补位后的明文和
func pkcs7decode(plaintext []byte) []byte {
ln := len(plaintext)
// 获取最后一个字符的 ASCII
pad := int(plaintext[ln-1])
if pad < 1 || pad > pkcs7BlockSize {
pad = 0
}
return plaintext[:(ln - pad)]
}
// 解压
// pkcs7Unpacked returns slice of the original data without padding
func Pkcs7Unpacked(data []byte, blockSize int) ([]byte, error) {
if blockSize <= 0 {
return nil, ErrInvalidBlockSize
}
if len(data)%blockSize != 0 || len(data) == 0 {
return nil, ErrInvalidPKCS7Data
}
c := data[len(data)-1]
n := int(c)
if n == 0 || n > len(data) {
return nil, ErrInvalidPKCS7Padding
}
for i := 0; i < n; i++ {
if data[len(data)-n+i] != c {
return nil, ErrInvalidPKCS7Padding
}
}
return data[:len(data)-n], nil
}