You can totally use emojis as passwords. You can probably even make this a policy at your company.
Edit: I thought this was an obvious enough joke, but just to clear things up: Only do this if you hate your company and everyone working there.
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NordPass is completely incorrect on the "it makes a password easier to "crack" thing.
I absolutely don't recommend using emojis in your password, as it is far too easy to get locked out. However, a password containing an emoji is significantly harder to crack.
Hashing is a process used to calculate a large number based on some input data. If the input is the same, the output is the same. If the input differs just slightly, the output is completely different. This process is mathematically irreversible. Since this (and other techniques) is often used for passwords, to "crack"/bruteforce a password, the attacker has to go through every possible combination of input data, calculate the hash, and check if the hash is the same as the password hash.
To make the process of bruteforcing a hash quicker, an attacker often makes assumptions about the input data. If they know a password contains 8 characters, and only lowercase letters, this massively narrows down the amount of passwords that need to be hashed and checked. If they know the password contains someones birth year, that too reduces the time to bruteforce a password.
The more possible characters you have per position in your password, the longer it will take to bruteforce. An 8 character password with just lowercase letters has 208.827.064.576 possible combinations. This sounds like a lot, but it's often bruteforced rather quickly. Adding uppercase letters and numbers to that, we're already at 218.340.105.584.896 possible combinations. That's ~1000x more combinations, and that's for 8 characters. It's the difference between bruteforcing taking a day, and taking 1000 days. (Do note an 8 characters lowercase password probably only takes like a few seconds to minutes, not a full day.)
According to https://emojipedia.org/stats there are 3664 different emojis. Lets say we create an 8 emoji password. (some emojis aren't one character internally, the same principle still applies.) Just 8 completely randomly chosen emojis. That password would have 32.482.071.647.592.311.234.920.185.856 different possible combinations. That is about 148.768.232.755.857 times more combinations than an 8 character uppercase+lowercase+numbers password. That is the difference between bruteforcing taking a day or taking 407584199331 years.
The same things as non-emoji passwords still apply, you can make assumptions about which emojis are used. People aren't entirely random, so chances are higher they used some of the more common emojis. However, that is similar to prioritizing the letter "e" because it is more common. Yes, it'll probably reduce the time taken to bruteforce a bunch of passwords, but it's not set in stone that every password will even contain the letter "e".
Again, due to the potential of breaking things, locking yourself out, etc. I DO NOT recommend using emojis. Use a password manager with longer passwords.
However, including an emoji in your password makes it significantly more difficult to bruteforce. As the assumption that the characters in your password are letters, numbers, and symbols no longer holds, which drastically increases the possible number of combinations.
For somewhat more realistic numbers:
According to minerstat.com, an NVidia RTX 4090 has a hashrate of 118.07MH/s. This is 118.07 Megahashes per second, or 118.070.000 hashes per second. For a password with only 8 lowercase letters (208.827.064.576 combinations), it would take an RTX 4090 approximately 1769 seconds (or ~30 minutes) to go through all possible combinations. For an 8 character upper+lower+numbers password (218340105584896 combinations) it would take 1849243 seconds, or 21.4 days.
For an 8 emoji password (32482071647592311234920185856 combinations), it would take 275.108.593.610.504.896.512 seconds, or 8.723.636.276.335 years.
Lets say a magic prediction algorithm reduces the number of possible combinations in each password to 1 out of every 1 million previously possible combinations. 8 lowercase letters would be cracked instantly, while an 8 emoji password would still take 8.723.636 years.
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The times I calculated were indeed going over every possible combination, it would take half as long to crack a password on average. Considering reducing the time to 1/1000000 still leaves you with an incomprehensibly large estimated timespan, dividing that by 2 doesn't do that much for making it brute-forceable.
I did note it was specifically for 8 emojis, not 8 characters or bytes.
And yes, it's very impractical and likely to break things. It's better and much easier to add extra letters, numbers, and symbols to your password rather than using emojis. Using a password manager is even better.
As you stated, a single unicode character would mean your password wouldn't be included with the potential options in almost all brute forcing tools. Whether you use 8 emojis or 1, your password likely won't get brute forced.
All of my "emoji password" numbers are if the attacker knows it's a password containing exactly 8 emojis, and nothing more. Adding a regular symbols+upper+lower+numbers 16 character password would make it even more impossible to brute force.