alt Hacker NewsRSA and Python
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I made a similar tutorial for RSA and DH in Easylang—a learning and teaching programming language I developed myself. What makes things a bit difficult is that Easylang doesn't support big numbers.
I have a different take on the same topic: https://www.nayuki.io/page/java-biginteger-was-made-for-rsa-...
My article isn't written as a step-by-step tutorial and doesn't come with example numbers. But mine fills in certain things that xnacly doesn't cover: random prime generation, efficiently calculating the decryption exponent d from (n, e) by using a modular inverse, using modular exponentiation instead of power-then-modulo.
By the way for Python, modular exponentiation is pow(x, y, m) (since 3.0), and modular inverse is pow(x, -1, m) (since 3.8, Oct 2019). https://docs.python.org/3/library/functions.html#pow
One of the bigger hurdles in implementing RSA is having an algorithm which can multiply the large numbers in real time. If you try a niave multiplication algorithm, you might find you'll never get an answer. A lot of hardware now comes with special instructions which implement efficient algorithms for doing this.
RSA is one of those algorithms where understanding it once actually sticks.
The way the article uses RSA is no better than a simple substitution cipher. Both the "l"s in "hello" are enciphered to 2575. It's a newspaper cryptogram.
You're supposed to concatenate all the input numbers, to create a message that has hundreds or thousands of digits; then RSA-encrypt that number.