Challenge 1: Convert hex to base64

Problem

Convert hex to base64

The string:
49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d

Should produce:
SSdtIGtpbGxpbmcgeW91ciBicmFpbiBsaWtlIGEgcG9pc29ub3VzIG11c2hyb29t

Solution

Strategy

• Convert hex to Decoded String
• Convert String to Base64

Explanation

First decoding our input hex encoded string to binary. To hex encode a string we break each byte of string into two 4 bits and then convert each 4 bits to hex. For example, Hello is encoded as 48656c6c6f in hex. The first byte 72 translate to 01001000 in binary splitting 4 bits at a time we get 0100 1000 which is 48 in hex.

hello := "Hello"
fmt.Println([]byte(hello))  //[72 101 108 108 111]

We have 49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d, first two characters 49 translates to 01001001 in binary, 73 in decimal and I in ASCII.

Now that we have decoded from hex encoding, we need to encode it to base64.

• We break it down into bytes and take 3 bytes of binary data and split it into 4 groups of 6 bits each.
• Each group of 6 bits is then converted to a character in the base64 alphabet.
• If the last bits come short of bits we pad it with =.

For example, I'm is represented by the bytes 73 39 109, which in binary is 01001001 00100111 01101101. Splitting this into groups of 6 bits gives 010010 010010 011101 101101 which translates to S S d t in base64.

Success

Code

package challenge1

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

func Challenge1() {
  // HEX Decode
  hexEncoded := []byte("49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d")

  hexDecoded := DecodeHex(hexEncoded)
  fmt.Printf("Hex Decoded: %s", hexDecoded)

  // Base64 Encode
  encoded := EncodeBase64(hexDecoded)
  fmt.Printf("\nBase64: %s", encoded)
}

func DecodeHex(input []byte) []byte {
  decoded := make([]byte, hex.DecodedLen(len(input)))

  _, err := hex.Decode(decoded, input)
  if err != nil {
    fmt.Printf("\nError:%s\n", err)
    return nil
  }
  return decoded
}

func EncodeHex(in []byte) []byte {
  encoded := make([]byte, hex.EncodedLen(len(in)))
  hex.Encode(encoded, in)
  return encoded
}

func EncodeBase64(input []byte) []byte {
  encoded := make([]byte, base64.StdEncoding.EncodedLen(len(input)))
  base64.StdEncoding.Encode(encoded, input)
  return encoded
}

func DecodeBase64(input []byte) []byte {
  decoded := make([]byte, base64.RawStdEncoding.DecodedLen(len(input)))
  _, err := base64.RawStdEncoding.Decode(decoded, input)
  if err != nil {
    fmt.Printf("\nError:%s\n", err)
    return nil
  }
  return decoded
}