How to generate a cryptographically secure random number in Go?

To generate a cryptographically secure random number in Go, you can make use of crypto/rand package. Here's an example on how to do it:

package main

import (
    "crypto/rand"
    "encoding/binary"
    "fmt"
)

func main() {
    // Create a byte slice to hold the random number
    numBytes := 8 // 8 bytes = 64 bits
    randBytes := make([]byte, numBytes)
    
    // Fill the byte slice with random data
    _, err := rand.Read(randBytes)
    if err != nil {
        fmt.Println("Error generating random number:", err)
        return
    }
    
    // Convert the byte slice to an integer
    randNum := binary.BigEndian.Uint64(randBytes)
    
    // Ensure the random number is positive
    if randNum < 0 {
        randNum = -randNum
    }
    
    // Print the random number
    fmt.Println("Random number:", randNum)
}

In this example, we generate a random number with 64 bits (8 bytes) of entropy. The rand.Read() function is used to fill the byte array with random data. Then, we convert the byte array to an unsigned 64-bit integer using binary.BigEndian.Uint64(). Finally, we ensure the random number is positive and print it to the console.

Note that crypto/rand library accesses a system-level random number generator, which provides a cryptographically secure source of randomness.