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The Way to Go

Cryptography with Go

Explore how to apply cryptographic techniques in Go using its standard library. Understand checksum computation, hash interfaces, and encryption methods to secure data in network communications and prevent unauthorized access.

We'll cover the following...

Introduction

A technique to secure data from the third parties over communication is called cryptography. The data transferred over networks must be encrypted so that no hacker can read or change it. Also, checksums calculated over the data, before sending and after receiving, must be identical. Given the business of its mother company Google, it will come as no surprise to see that Go has more than 30 packages to offer in this field, all contained in its standard library:

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  • hash package: implements the adler32, crc32, crc64 and fnv checksums
  • crypto package: implements other hashing algorithms like md5, sha1, and so on and complete encryption implementations for aes, rc4, rsa, x509, and so on.

Example

In the following program, we compute and output some checksums with sha1:

Go (1.6.2)
package main
import (
"fmt"
"crypto/sha1"
"io"
"log"
)
func main() {
  hasher := sha1.New()
  io.WriteString(hasher, "test")
  b := []byte{}
  fmt.Printf("Result: %x\n", hasher.Sum(b))
  fmt.Printf("Result: %d\n", hasher.Sum(b))
  hasher.Reset()
  data := []byte("We shall overcome!")
  n, err := hasher.Write(data)
  if n!=len(data) || err!=nil {
    log.Printf("Hash write error: %v / %v", n, err)
  }
  checksum := hasher.Sum(b)
  fmt.Printf("Result: %x\n", checksum)
}

In the code above, we import the package crypto/sha1 at line 4. At line 10, we make a new instance hasher of sha1, which we use at line 11 to encrypt the string test.

With sha1.New(), a new hash.Hash object is made to compute the SHA1 checksum. The type Hash is, in fact, an interface, itself implementing the io.Writer interface:

type Hash interface {
  // Write adds more data to the running hash.
  // It never returns an error.
  io.Writer
  // Sum returns the current hash, without changing the
  // underlying hash state.
  Sum() []byte

  // Reset resets the hash to one with zero bytes written.
  Reset()
  // Size returns the number of bytes Sum will return.
  Size() int
}

Through io.WriteString or hasher.Write, the checksum of the given string is computed. This is first done for test at line 13 and line 14, the respective outputs are:

Result: a94a8fe5ccb19ba61c4c0873d391e987982fbbd3
Result: [169 74 143 229 204 177 155 166 28 76 8 115 211 145 233 135 152 47 187 211]

The hasher.Write is used at line 17 to encrypt We shall overcome! After error-handling (from line 18 to line 20), we calculate the checksum and print it out:

Result: e2222bfc59850bbb00a722e764a555603bb59b2a

That is how Golang implements cryptography on data with its packages to make data secure. There is a quiz in the next lesson for you to solve.