The WW2 German Enigma cipher machine has 158,962,555,217,826,360,000 different possibilities (nearly 159 quintillion). The BIP39 seed phrase word list contains 2,048 words, so a 12-word crypto seed phrase has about 2 to the power of 132 possible combinati

It's also a larger number than the number of atoms in the universe. I wrote a post recently on tips to memorize your seed phrase ( Disclaimer: The "wet wallet" inside your skull is the one of last resort) and in looking at BIP39 on GitHub I realized what a thing of beauty it is. Quick background: Although Bitcoin is often called "Grandpa" as the OG cryptocurrency, it's still undergoing continual development.

Bitcoin Improvement Proposal 39 "describes the implementation of a mnemonic code or mnemonic sentence -- a group of easy to remember words -- for the generation of deterministic wallets." Essentially, BIP39 represents the binary number of a wallet as words, with the logic being it's more difficult to write down (or remember) a long abstract number versus words, which are much easier.

It's difficult though to comprehend how vanishingly unlikely it is for modern computing power to be able to guess a 12 word phrase by brute force calculation. There's been many estimates made, but the one I favour is that it would take 2.21 trillion billion years to crack a 12 word seed at current computing power … another estimate I’ve seen says it would take a trillion computers, guessing a trillion times a second, for the lifetime of the universe.

What about quantum computers? It's still very early days:

"According to Mark Webber at the University of Sussex in the U.K., breaking this level of encryption would reportedly require a quantum computer with 1.9 billion “qubits." This is a staggeringly high figure, especially when you consider that IBM’s best quantum computer boasts a mere 127 quibits in comparison."

So we're golden at the moment.

Sources:

https://decrypt.co/resources/is-quantum-computing-threat-bitcoin

https://en.bitcoin.it/wiki/BIP_0039