Be careful with hashmaps

As you remember from long ago hashes are O(1) best case, but can be O(n) if you get hash collisions. And if you're adding n new entries that means O(n^2).

I thought I'd take a look at the hash_set/hash_map GNU C++ extension.

Benchmarking TPM-backed SSL

As you can plainly see from this graph, my TPM chip can do approximately 1.4 SSL handshakes per second. A handshake takes about 0.7 seconds of TPM time, so when two clients are connecting the average connect time is 1.4 seconds. This means probably not useful on server side, but should be good for some client side applications.

TPM-backed SSL

This is a short howto on setting up TPM-backed SSL. This means that the secret key belonging to an SSL cert is protected by the TPM and cannot be copied off of the machine or otherwise inspected.

Meaning even if you get hacked the attackers cannot impersonate you, if you manage to kick them off or just shut down the server. The secret key is safe. It has never been outside the TPM and never will be.

This can be used for both client and server certs.

Secure browser-to-proxy communication

When connecting to a possibly hostile network I want to tunnel all traffic from my browser to some proxy I have set up on the Internet.

The obvious way to do this is with a proxy. The problem with that is that the traffic from the browser to the proxy is not encrypted. Even when you browse to secure SSL sites some traffic is being sent in the clear, such as the host name. That's not so bad, but I want to hide my HTTP traffic too.

Optimizing TCP slow start

The short version of the problem and solution I will describe is that while TCP gets up to speed fairly fast, and "fast enough" for many uses, it doesn't accelerate fast enough for short-lived connections such as web page requests. If I have 10Mbps connection and the server has 10Mbps to spare, why doesn't a 17kB web page transfer at 10Mbps from first to last byte? (that is, when excluding TCP handshake, HTTP request and server side page rendering)

This is pretty Linux-focused, but I'll add pointers for other OSs if I see them.

Yubico is awesome

Yubico and their products are awesome.

That pretty much sums up this blog post but I'm going to go on anyway. If you're thinking of introducing two-factor authentication to your company, or you're using something that's fundamentally broken (like RSA SecureID) you simply must at least take Yubikeys into consideration.

OpenSSH certificates

The documentation for OpenSSH certificates (introduced in OpenSSH 5.4) are, shall we say, a bit lacking. So I'm writing down the essentials of what they are and how to use them.

What they are NOT

They're not SSH PubkeyAuthentication

In other words if your .pub file doesn't end in -cert.pub and you haven't used ssh-keygen -s, then you aren't using certificates.

gettimeofday() should never be used to measure time

gettimeofday() and time() should only be used to get the current time if the current wall-clock time is actually what you want. They should never be used to measure time or schedule an event X time into the future.

tlssh - a replacement for SSH

I've started writing a replacement for SSH.

Why? Because SSH has some drawbacks that sometimes annoy me. I also wanted an authentication scheme that's more similar to SSL/TLS than what SSH does.

With tlssh you don't specify username or password, you simply connect to the server using a client-side certificate to log in as the user specified in the certificate. No interaction until you reach the shell prompt on the server.

The rules of multicast

The first rule of multicast is you don't talk about multicast

Most networks don't do multicast routing, which means most network guys don't have much experience with it. Sure they know that it exists, and it's probably used on their layer 2, but they don't do multicast routing. These "rules" list some things that you should know when configuring or troubleshooting multicast.