53 lines
1.4 KiB
Go
53 lines
1.4 KiB
Go
package logcodec
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import (
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"crypto/cipher"
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"crypto/des"
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"encoding/base64"
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"errors"
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"fmt"
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)
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var (
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policyKey = []byte("hyhccdtm")
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policyIV = []byte{0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF}
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)
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func DecryptLine(ciphertextBase64 string) (string, error) {
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ciphertext, err := base64.StdEncoding.DecodeString(ciphertextBase64)
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if err != nil {
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return "", fmt.Errorf("decode base64 log line: %w", err)
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}
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if len(ciphertext) == 0 || len(ciphertext)%des.BlockSize != 0 {
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return "", fmt.Errorf("ciphertext length %d is not a positive DES block multiple", len(ciphertext))
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}
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block, err := des.NewCipher(policyKey)
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if err != nil {
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return "", fmt.Errorf("create DES cipher: %w", err)
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}
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plain := make([]byte, len(ciphertext))
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cipher.NewCBCDecrypter(block, policyIV).CryptBlocks(plain, ciphertext)
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plain, err = unpadPKCS7(plain, des.BlockSize)
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if err != nil {
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return "", err
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}
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return string(plain), nil
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}
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func unpadPKCS7(data []byte, blockSize int) ([]byte, error) {
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if len(data) == 0 || len(data)%blockSize != 0 {
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return nil, errors.New("pkcs7 data is empty or not block aligned")
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}
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pad := int(data[len(data)-1])
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if pad == 0 || pad > blockSize || pad > len(data) {
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return nil, fmt.Errorf("invalid pkcs7 padding length %d", pad)
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}
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for i := len(data) - pad; i < len(data); i++ {
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if int(data[i]) != pad {
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return nil, errors.New("invalid pkcs7 padding bytes")
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}
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}
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return data[:len(data)-pad], nil
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}
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