go/cryptojs/pkcs7.go

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package cryptojs
import (
"bytes"
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"fmt"
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)
// Appends padding.
func pkcs7Pad(data []byte, blocklen int) ([]byte, error) {
if blocklen <= 0 {
return nil, fmt.Errorf("invalid blocklen %d", blocklen)
}
padlen := uint8(1)
for ((len(data) + int(padlen)) % blocklen) != 0 {
padlen++
}
if int(padlen) > blocklen {
panic(fmt.Sprintf("generated invalid padding length %v for block length %v", padlen, blocklen))
}
pad := bytes.Repeat([]byte{byte(padlen)}, int(padlen))
return append(data, pad...), nil
}
// Returns slice of the original data without padding.
func pkcs7Unpad(data []byte, blocklen int) ([]byte, error) {
if blocklen <= 0 {
return nil, fmt.Errorf("invalid blocklen %d", blocklen)
}
if len(data)%blocklen != 0 || len(data) == 0 {
return nil, fmt.Errorf("invalid data len %d", len(data))
}
padlen := int(data[len(data)-1])
if padlen > blocklen || padlen == 0 {
// Not padded
return data, nil
}
// check padding
pad := data[len(data)-padlen:]
for i := 0; i < padlen; i++ {
if pad[i] != byte(padlen) {
return data, nil
}
}
return data[:len(data)-padlen], nil
}