It should be obvious that you should never share the PSK with anyone. Pre-shared keys, no matter their length, have no effect on performance. The Diffie-Hellman key exchange may be secure, but it’s not going to matter if your pre-shared key is 12345.Īnother note: don’t use the same pre-shared key across different phase 1 configurations. Therefore, it’s important to pick a pre-shared key that’s relatively secure this means no dictionary words, at least a few symbols, a few numbers, and a minimum of 15 characters. You could even set it to as long as months (if your hardware supported it), but as we’re concerned with security and not performance in phase 1, 24 hours is acceptable.Īlthough certificates can be used and are more secure, no one ever wants to go through the hassle of setting up a key infrastructure dedicated to IPsec usage. When using a decent hashing and encryption method, any key life under 24 hours is more than adequate, as no one will be able to brute force your key in that amount of time. However, most people use timing instead of byte counts. For one, you can forgo timing altogether and set it as a byte count - once x amount of bytes has been processed through the tunnel, it will renegotiate. Key lifetime is an interesting parameter. Also, AES256 is logically slower than AES128. Note: AES256 is even more secure, but the additional security afforded by jumping to 256 bits is similar to comparing the thickness of two pieces of paper: it’s there, but for all practical purposes there’s no difference. AES128 is considered to be secure today and for the foreseeable future. Remember: using less processing per packet lets more packets be encrypted, which translates into increased throughput.ĪES comes in a number of key size variants, starting at AES128. Another bonus: AES is hardware-accelerated on a wide variety of processors, making it even quicker while using less processing power. Not only is AES far faster than 3DES, it’s also considered more secure. Instead, more modern algorithms should be used, particularly the Advanced Encryption Standard (AES) suite. Though these encryption algorithms can still can be used, they are highly discouraged. Triple DES (3DES) came in to replace it and is still in use today, but it’s terribly slow. While simple and fast, it was easily broken, and became obsolete in 1999. Data Encryption Standard (DES) used to be the standard. There are a number of algorithms for encrypting traffic. Newer hashing options include SHA variations with larger bits, such as SHA-256, SHA-384, and SHA-512. This disables hashing (and at that point, you may as well not even bother with an IPsec tunnel). Never use this - it’s only included in the IPsec standard as a testing mechanism. Given phase 1 is focused more on security, we opt for the slower but more secure SHA1. SHA1 is considered even more secure, at the cost of some computational overhead (i.e., it’s slower than MD5). While vanilla MD5 has been proven broken, HMAC-MD5 is still considered secure. IPsec tunnels use keyed-hash message authentication code (HMAC) versions of these algorithms. The two common hashing options for IPsec are MD5 and SHA1. Hashes are designed so that even tiny changes in a packet will radically alter the hash, and are extremely difficult (if not impossible) to reverse engineer. If the packet is changed in transit, the resulting hash will no longer match the computed value. When it arrives at its destination, the hash is re-run. A hash is simply a mathematical operation that runs on a dataset (in this case, a single IP packet) and generates a unique string. These days, that list could be endless your transit providers, any state agencies with taps into transit networks, hackers who have secured access to routing and switching equipment, or even employees with or without ill intent.Ī correctly implemented hash can negate this threat. On the public internet, “nefarious parties” could be anyone that could theoretically view the data stream. Without hashing, a nefarious party could throw a bunch of garbage into your packets and there’d be no way of knowing - even if your data is encrypted. You want to make sure the packet you sent is the packet that arrived. This is important for secure communications. Hashing algorithms are for verifying data integrity, not encryption. Note that something that decreases security doesn’t necessarily increase speed - these are two separate and independent metrics. Certain options increase security, and certain options increase speed. The answer is simple: speed and security. So, why did we choose those particular parameters? This week, let’s get into the nitty gritty of why those parameters were chosen. On the previous episode of As The IPsec Tunnel Churns, we discussed how IPsec configurations running in tunnel mode are established.
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