crypt.go

package main

import (
        "crypto/aes"
        "crypto/cipher"
        "crypto/rand"
        "crypto/sha256"
        "fmt"
        "io"
        "os"
        "regexp"
        "slices"
        "strings"
)

func main() {
        fmt.Print("\n\033[1;34mPasskey : \033[0m")
        var keyString string
        fmt.Scan(&keyString)
        fmt.Println()

        h := sha256.New()
        h.Write([]byte(keyString))
        key := h.Sum(nil)

        file := "./crypt.log";
        plainText := ""
        cipherText, err := os.ReadFile(file)
        if err == nil {
                plainText, err = DecryptMessage(key, cipherText)
                if err != nil { panic(err) }
        }

        for {
                fmt.Print("\033[1;34mCommand : \033[0m")
                var command string
                fmt.Scan(&command)

                switch command {
                        case "get":
                                var arg string
                                fmt.Scan(&arg)
                                fmt.Println(strings.Join(regexp.MustCompile(arg + `(.*)?\n`).FindAllString(plainText, -1), ""))
                        case "set":
                                var argk string
                                fmt.Scan(&argk)
                                var argv string
                                fmt.Scan(&argv)
                                re := regexp.MustCompile(argk + ` (.*)?\n`)
                                if re.MatchString(plainText) {
                                        plainText = re.ReplaceAllString(plainText, argk + " " + argv + "\n")
                                } else {
                                        plainText += argk + " " + argv + "\n"
                                }
                                lines := strings.Split(plainText, "\n")
                                lines = lines[:len(lines) - 1]
                                slices.Sort(lines)
                                plainText = strings.Join(lines, "\n") + "\n"
                                fmt.Println()
                        case "del":
                                var arg string
                                fmt.Scan(&arg)
                                re := regexp.MustCompile(arg + ` (.*)?\n`)
                                plainText = re.ReplaceAllString(plainText, "")
                                fmt.Println()
                        case "show":
                                fmt.Println(plainText)
                        case "list":
                                re := regexp.MustCompile(` (.*)?\n`)
                                fmt.Println(re.ReplaceAllString(plainText, "\n"))
                        case "save":
                                cipherText, err := EncryptMessage(key, plainText)
                                if err != nil { panic(err) }
                                err = os.WriteFile(file, cipherText, 0644)
                                if err != nil { panic(err) }
                                fmt.Println()
                        case "quit":
                                fmt.Println()
                                return
                        default:
                                fmt.Println("Invalid Command\n")
                }
        }

}

func EncryptMessage(key []byte, message string) ([]byte, error) {
        byteMsg := []byte(message)
        block, err := aes.NewCipher(key)
        if err != nil { panic(err) }

        cipherText := make([]byte, aes.BlockSize+len(byteMsg))
        iv := cipherText[:aes.BlockSize]
        _, err = io.ReadFull(rand.Reader, iv)
        if err != nil { panic(err) }

        // https://pkg.go.dev/crypto/cipher#NewCFBEncrypter
        stream := cipher.NewCFBEncrypter(block, iv)
        stream.XORKeyStream(cipherText[aes.BlockSize:], byteMsg)

        return cipherText, nil
}

func DecryptMessage(key []byte, cipherText []byte) (string, error) {
        block, err := aes.NewCipher(key)
        if err != nil { panic(err) }

        if len(cipherText) < aes.BlockSize {
                return "", fmt.Errorf("invalid ciphertext block size")
        }

        iv := cipherText[:aes.BlockSize]
        cipherText = cipherText[aes.BlockSize:]

        // https://pkg.go.dev/crypto/cipher#NewCFBDecrypter
        stream := cipher.NewCFBDecrypter(block, iv)
        stream.XORKeyStream(cipherText, cipherText)

        return string(cipherText), nil
}

crypt.md

The attached Go script is a minimal secret management utility to securely note personal data such as usernames & passwords.

The CLI application can be started with a simple go run crypt.go. It provides read-write interface to work with space-separated key value lines using commands get <key-prefix>, set <key> <value>, del <key>, show, list, save, quit.

The application requires a central key on startup, & loads any previously saved data. The plain text & central key stay in process memory, and only AES-256 encrypted cipher text is written to storage. The cipher text can be replicated across devices or uploaded to personal cloud drive.

The script can also be tweaked slightly to capture encrypted timed logs instead of key-value pairs,

package main

import (
        "bufio"
        "crypto/aes"
        "crypto/cipher"
        "crypto/rand"
        "crypto/sha256"
        "fmt"
        "io"
        "os"
        "strings"
        "time"
)

func main() {
        .
        .
        .
        fmt.Print("\033[1;34mUser : \033[0m")
        var user string
        fmt.Scan(&user)
        fmt.Println()

        rd := bufio.NewReader(os.Stdin)
        for {
                fmt.Print("\033[1;34m> \033[0m")
                var command string
                command, err := rd.ReadString('\n')
                if err != nil { panic(err) }
                
                switch strings.Fields(command)[0] {
                        case ":r":
                                fmt.Println(plainText)
                        case ":w":
                                cipherText, err := EncryptMessage(key, plainText)
                                if err != nil { panic(err) }
                                err = os.WriteFile(file, cipherText, 0644)
                                if err != nil { panic(err) }
                                fmt.Println()
                        case ":q":
                                fmt.Println()
                                return
                        default:
                                plainText += "\n\033[1;35m[" + time.Now().Format("06-01-02_03:04:05PM") + "] " + user + " >\033[0m " + command;
                                fmt.Println()
                }
        }
}
.
.
.