A typical HTTP request looks like this:Īs with many other attacks against HTTPS, Sweet32 requires an attacker that can inject JavaScript code into any page open in a user’s browser and observe network traffic generated by the browser executing the injected JavaScript code. Now, let’s take a look at the Sweet32 attack as it applies to HTTPS connections. In general, given a set of randomly selected objects, each with a property that can have one of 2^ n values that are equally likely, we have a 50% likelihood of seeing multiple objects with the same property after selecting approximately 2^( n/2) objects.Īpplying this to 3DES (or any 64-bit block cipher) operating in CBC mode, this means that after observing only about 2^32 (i.e., 4.3 billion) blocks of ciphertext, we are likely to see two identical blocks of ciphertext. Here is a chart that shows the probability of shared birthdays for N between 2 and 70: This turns out to be much lower than most people would intuitively believe. Given several assumptions (e.g., all birthdays are equally likely, ignoring leap years, etc.), it turns out that for N = 23, the probability of a shared birthday is 50%. The birthday paradox is about the probability of at least two people sharing the same birthday in a room containing N people who are chosen at random. To understand this, we need to also understand the birthday paradox. What does this mean in terms of security? Birthday paradox The result is an encryption algorithm with an effective key strength of 112 bits, which is still considered secure against brute-force attacks today.Īlthough a 112-bit key strength is sufficient to protect against brute-force attacks, 3DES suffers from a potential problem: it operates on 64-bit blocks of data. 3DES involves performing three DES operations to encrypt/decrypt each 64-bit block of data using either two or three distinct 56-bit keys. However, as it became feasible to brute-force 56-bit keys, 3DES was adopted as a standard in the 1990s. The algorithm uses 56-bit keys, which were long enough to be secure at the time. It was adopted as a FIPS standard in 1977. The DES encryption algorithm was designed in the early 1970s by researchers at IBM.

How long does it take to crack 3des