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diff --git a/src/content/blogs/the-search-for-the-perfect-ssh-key.mdx b/src/content/blogs/the-search-for-the-perfect-ssh-key.mdx new file mode 100644 index 0000000..215a411 --- /dev/null +++ b/src/content/blogs/the-search-for-the-perfect-ssh-key.mdx @@ -0,0 +1,117 @@ +--- +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`, other common algorithms are `ssh-rsa` and `ssh-ecdsa`. +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! |