Stefan Alfbo

Posted on

# Convert hex to base64

This is the first crypto challenge in set 1 from cryptopals, which is the qualifying set.

The difficulty level is relatively easy, to solve this problem I have used the programming language Go.

# Problem description

Convert a string with hex values to a base64 string. The rules are:

Always operate on raw bytes, never on encoded strings. Only use hex and base64 for pretty-printing.

The input is:

`49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d`

which should give the following output

`SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t`

# Solution

The go language has great support for this kind of problems through their standard libraries in `encoding` package.

There are two of interest in this case.

``````import (
"encoding/base64"
"encoding/hex"
)
``````

The names of these packages are pretty much self-explanatory, `base64` implements base64 encoding and `hex` implements hexadecimal encoding and decoding.

First step is to convert the hexadecimal string to a slice of bytes. The `hex` package has a perfect function for this, `DecodeString`, which takes a hexadecimal string.

``````    bytes, err := hex.DecodeString(theString)
if err != nil {
return
}
``````

The last step of the problem is to encode this slice of bytes to base64. Naturally we will look after a good function for this job in the `base64` package. There are two candidates for this, `EncodeToString` and `Encode`. We will go with `EncodeToString`, since we want to print a string to see if we got the correct result.

``````str := base64.StdEncoding.EncodeToString(bytes)
``````

Now we have all the pieces to solve the problem, and the program could look like this.

``````package main

import (
"encoding/base64"
"encoding/hex"
"fmt"
)

func convertToBase64(hexString string) (string, error) {
bytes, err := hex.DecodeString(hexString)
if err != nil {
return "", err
}

return base64.StdEncoding.EncodeToString(bytes), nil
}

func main() {
theString := "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d" // Replace with your hex string

str, err := convertToBase64(theString)
if err != nil {
return
}

fmt.Println("Base64:", str)
}
``````

# Conclusion

The problem is easy to solve when having access to Go's standard packages and its great documentation.