pkcs#7.go

import (
    "bytes"
    "fmt"
)

// Appends padding.
func pkcs7Pad(data []byte, blocklen int) ([]byte, error) {
    if blocklen <= 0 {
        return nil, fmt.Errorf("invalid blocklen %d", blocklen)
    }
    padlen := 1
    for ((len(data) + padlen) % blocklen) != 0 {
        padlen = padlen + 1
    }

    pad := bytes.Repeat([]byte{byte(padlen)}, 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 {
        return nil, fmt.Errorf("invalid padding")
    }
    // check padding
    pad := data[len(data)-padlen:]
    for i := 0; i < padlen; i++ {
        if pad[i] != byte(padlen) {
            return nil, fmt.Errorf("invalid padding")
        }
    }

    return data[:len(data)-padlen], nil
}