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+---
+title: The search for the perfect SSH key
+description: How you can embed your name in an SSH key
+date: 2024-11-15
+---
+
+SSH keys are a widely used tool among developers,
+they are the equivalent of a username and password in the development world.
+They allow you to prove your identity and they are the gateway
+into accessing servers remotely in a secure manner.
+
+## The SSH public key format
+
+When generating an ssh key, you get 2 files, one with no extension that stores the private key
+and another that ends with a `.pub`.
+The public key is what you share publicly on your profile or add to a remote server to login through SSH.
+
+Here's how a typical SSH public key looks
+
+```
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBSSj+yfJLWEb+Df4r4603TOFAUBREYS43qQB+c9i9UW
+```
+
+It consists of 2 parts, the algorithm, in this case it's
+`ssh-ed25519`, but it can be other ones too such as `ssh-rsa`.
+The second part is a base64 encoded custom binary format.
+
+Let's break it down
+
+- the length of the algorithm string, for ed25519 it's always 11 (4 bytes long)
+- the algorithm type, for ed25519 it's always `ssh-ed25519` in binary (11 bytes long)
+- the length of the key, 32 bytes for ed25519 (4 bytes long)
+- the raw bytes for the ed25519 key (32 bytes long)
+
+## Embedding a word in base64
+
+Base64 is a widely used format for displaying binary in a compact and human readable way,
+it uses A-Z, a-z, 0-9, '/' and '+' adding up to 64 unique characters.
+
+It's possible to choose specific bytes in a way that when encoding it with base64
+it will form a word.
+
+For example, to encode "Kyren" in base64, we can use the bytes  
+`00101011 00101010 01001110` or in hex `2b 2a de`.
+
+So by controlling the 32 bytes at the end of the ssh we are able to get
+a ssh public key containig any keyword we want.
+
+## Brute Force
+
+Unfortunately this approach won't work, we still want to be able to use the key
+so we will need to know the corresponding private key, but it's impossible to reverse engineer
+the private key using the public one, that's why cryptography is so secure.
+
+The solution is simple, just generate a bunch of keys until we get lucky and find the desired keyword.
+So that's what I have done, here's a basic go program that does exactly that.
+
+```go
+package main
+
+import (
+	"bytes"
+	"crypto/ed25519"
+	"encoding/base64"
+	"fmt"
+
+	"golang.org/x/crypto/ssh"
+)
+
+func main() {
+	keyword := []byte("Kyren")
+	for {
+		pubKey, privKey, _ := ed25519.GenerateKey(nil)
+		sshPubKey, _ := ssh.NewPublicKey(pubKey)
+		pub := ssh.MarshalAuthorizedKey(sshPubKey)
+		if bytes.Contains(pub, keyword) {
+			privBase64 := base64.StdEncoding.EncodeToString(privKey)
+			fmt.Printf("Found %s in %s with private key %s\n", string(keyword), string(pub), privBase64)
+			break
+		}
+	}
+}
+```
+
+I have later improved this program by adding multithreading and made it easier to use.
+The final code is available on my GitHub [at this link](https://github.com/Kyren223/ed25519-key-gen).
+
+## Results
+
+After running it for 2 days (about 24 hours in total) on my AMD Ryzen 5 7530U laptop (12 threads),
+here are the results:
+
+```
+Completed Search
+Time Elapsed: 12h9m11.225248108s
+Searched: 6733606724 Found: 737
+```
+
+- Generated and searched 150k SSH keys per second
+- Found a 5-character keyword every 9.1 million keys or about 1 every minute
+- Found a 6 character keyword every 1/64 of every 5-character keyword, or about 1 every hour
+- Found 5-character that are at the end of the SSH key 1/50 of every 5-character keyword
+
+My goal was to find a `/kyren` at the end of the key,
+on average that'd be 1 every 3200 5-character keywords.
+
+At the end after only 1862 keywords I found the key, here it is
+
+```
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIO7P9K9D5RkBk+JCRRS6AtHuTAc6cRpXfRfRMg/Kyren
+```
+
+I hope this inspires you to try and find your own SSH key,
+hopefully your name is not 7 characters long,
+and if it's 8, I hope you have 170 years to spare.
+
+Thanks for reading! this is my first blog post so any feedback will be appreciated!