If anyone would like to practice some of these lessons in a "capture the flag" format, I would recommend https://cryptohack.org/ -- great site! - Source: Hacker News / 2 months ago

Another similar website for people who like this: https://cryptohack.org/ It is like cryptopals, but in a Catch The Flag format. Many challenges on cryptopals do exist on CryptoHack too, but CryptoHack also have some even harder challenges to solve. - Source: Hacker News / about 1 year ago

The point is, you're working with a 200-year old manual cipher method. The field of cryptography has thoroughly perforated it and moved past manual ciphers and machine ciphers and onto mathematical ciphers whose strength is in functions whose inverses are astronomically more difficult to compute than the functions themselves, and key generation schemes that ensure that keys are never repeated no matter how many... Source: about 1 year ago

Cryptohack.org Platform for learning modern cryptography (Cryptohack). Source: over 1 year ago

CryptoHack : Learn cryptography through challenges and tutorials. Has a leaderboard and new challenges are added every few months. - Source: dev.to / over 1 year ago

Also just heard of this in another post if you need to expand your network. Source: almost 2 years ago