Hey there, crypto champion! Ready to dive into the world of digital signatures? Think of these as your digital autograph - a way to prove you're really you in the digital world, and that your message hasn't been tampered with. Let's explore how Go helps us create these unforgeable digital John Hancocks!

RSA Signatures: The Classic Autograph

First up, we've got RSA signatures. It's like signing a document with a really fancy, unforgeable pen.

import (
    "crypto"
    "crypto/rand"
    "crypto/rsa"
    "crypto/sha256"
    "fmt"
)

func main() {
    // Let's create our special signing pen (RSA key pair)
    privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
    if err != nil {
        panic("Oops! Our pen ran out of ink.")
    }
    publicKey := &privateKey.PublicKey

    // Our important message
    message := []byte("I solemnly swear that I am up to no good.")

    // Let's create a fingerprint of our message
    hash := sha256.Sum256(message)

    // Time to sign!
    signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA256, hash[:])
    if err != nil {
        panic("Our hand cramped while signing!")
    }

    fmt.Printf("Our RSA signature: %x\n", signature)

    // Now, let's verify our signature
    err = rsa.VerifyPKCS1v15(publicKey, crypto.SHA256, hash[:], signature)
    if err != nil {
        fmt.Println("Uh-oh, someone forged our signature!")
    } else {
        fmt.Println("Signature checks out. Mischief managed!")
    }
}

ECDSA Signatures: The Curvy Autograph

Next, we have ECDSA signatures. It's like RSA's cooler, more efficient cousin - smaller signatures with the same level of security.

import (
    "crypto/ecdsa"
    "crypto/elliptic"
    "crypto/rand"
    "crypto/sha256"
    "fmt"
    "math/big"
)

func main() {
    // Let's create our curvy signing pen
    privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
    if err != nil {
        panic("Our curvy pen got a bit too curvy!")
    }
    publicKey := &privateKey.PublicKey

    // Our important message
    message := []byte("Elliptic curves are mathematically delicious!")

    // Create a fingerprint of our message
    hash := sha256.Sum256(message)

    // Time to sign with our curvy pen!
    r, s, err := ecdsa.Sign(rand.Reader, privateKey, hash[:])
    if err != nil {
        panic("Our hand slipped while signing these curves!")
    }

    signature := append(r.Bytes(), s.Bytes()...)
    fmt.Printf("Our curvy ECDSA signature: %x\n", signature)

    // Let's verify our curvy signature
    r = new(big.Int).SetBytes(signature[:len(signature)/2])
    s = new(big.Int).SetBytes(signature[len(signature)/2:])
    valid := ecdsa.Verify(publicKey, hash[:], r, s)
    fmt.Printf("Is our curvy signature valid? %v\n", valid)
}

Ed25519 Signatures: The Speed Demon Autograph

Finally, we have Ed25519 signatures. These are like the sports car of digital signatures - fast and secure.

import (
    "crypto/ed25519"
    "crypto/rand"
    "fmt"
)

func main() {
    // Let's create our speedy signing pen
    publicKey, privateKey, err := ed25519.GenerateKey(rand.Reader)
    if err != nil {
        panic("Our speedy pen got a speeding ticket!")
    }

    // Our important message
    message := []byte("Speed is my middle name!")

    // Time to sign at lightning speed!
    signature := ed25519.Sign(privateKey, message)

    fmt.Printf("Our speedy Ed25519 signature: %x\n", signature)

    // Let's verify our speedy signature
    valid := ed25519.Verify(publicKey, message, signature)
    fmt.Printf("Is our speedy signature valid? %v\n", valid)
}

Choosing Your Perfect Signature

Now, you might be wondering, "Which signature should I use?" Well, it depends on your needs:

RSA: It's like the Swiss Army knife of signatures. Widely supported, but the signatures are a bit chunky.
ECDSA: It's the middle ground. Smaller signatures than RSA, still widely supported.
Ed25519: The new kid on the block. Super fast, small signatures, but might not be supported everywhere yet.

The Golden Rules of Digital Signatures

Now that you're a signature artist, here are some golden rules to keep in mind:

Randomness is key: Always use crypto/rand for anything related to signatures. Predictable randomness is like using the same signature every time - not good!
Hash before you sign: Except for Ed25519, always hash your message before signing. It's like creating a unique fingerprint of your message.
Size matters: Use at least 2048 bits for RSA, 256 bits for ECDSA, and Ed25519 is always 256 bits.
Keep your pens safe: Protect your private keys like you'd protect your most precious possessions. A stolen signing key is like someone stealing your identity!
Verify your verifiers: Make sure the public keys you're using to verify signatures are legit. A fake public key could make you trust a fake signature!
Standardize when possible: Consider using formats like JSON Web Signature (JWS) if you need to play nice with other systems.
Be aware of sneaky attacks: In high-security scenarios, watch out for side-channel attacks. They're like someone peeking over your shoulder while you sign.

What's Next?

Congratulations! You've just added digital signatures to your cryptographic toolkit. These are crucial for proving authenticity and integrity in the digital world.

Next up, we'll explore how Go handles TLS and X.509 certificates. It's like learning how to create and verify digital ID cards - essential for secure communication on the internet!

Remember, in the world of cryptography, understanding these basics is crucial. It's like learning to write your signature - a fundamental skill in the digital age. Master these, and you'll be well on your way to creating secure, authenticated applications in Go.

So, how about you try implementing a simple document signing system? Or maybe create a program that verifies software updates using digital signatures? The world of unforgeable digital autographs is at your fingertips! Happy coding, crypto champion!

Digital Signatures: Your Cryptographic John Hancock, Go Crypto 6