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.
“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.
if err != nil {
fmt.Println(“Error decoding hexadecimal string:”, err)
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.
Now we have all the pieces to solve the problem, and the program could look like this.
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 {
fmt.Println(“Error decoding hexadecimal string:”, err)
return
}
fmt.Println(“Base64:”, str)
}
Conclusion
The problem is easy to solve when having access to Go’s standard packages and its great documentation.
References
Set 1 – Challenge 1
The Base16, Base32, and Base64 Data Encodings
encoding/base64
encoding/hex
