GHSA-9hc7-6w9r-wj94

# Reduced entropy due to inadequate character set usage

## Description

Affected versions of the nano-id crate incorrectly generated IDs using a reduced character set in the `nano_id::base62` and `nano_id::base58` functions. Specifically, the `base62` function used a character set of 32 symbols instead of the intended 62 symbols, and the `base58` function used a character set of 16 symbols instead of the intended 58 symbols. Additionally, the `nano_id::gen` macro is also affected when a custom character set that is not a power of 2 in size is specified.

It should be noted that `nano_id::base64` is not affected by this vulnerability.

## Impact

This can result in a significant reduction in entropy, making the generated IDs predictable and vulnerable to brute-force attacks when the IDs are used in security-sensitive contexts such as session tokens or unique identifiers.

## Patches

The flaws were corrected in commit [a9022772b2f1ce38929b5b81eccc670ac9d3ab23](https://github.com/viz-rs/nano-id/commit/a9022772b2f1ce38929b5b81eccc670ac9d3ab23) by updating the the `nano_id::gen` macro to use all specified characters correctly.

## PoC

```rust use std::collections::BTreeSet;

fn main() { test_base58(); test_base62(); }

fn test_base58() { let mut produced_symbols = BTreeSet::new();

for _ in 0..100_000 { let id = nano_id::base58::<10>(); for c in id.chars() { produced_symbols.insert(c); } }

println!( "{} symbols generated from nano_id::base58", produced_symbols.len() ); }

fn test_base62() { let mut produced_symbols = BTreeSet::new();

for _ in 0..100_000 { let id = nano_id::base62::<10>(); for c in id.chars() { produced_symbols.insert(c); } }

println!( "{} symbols generated from nano_id::base62", produced_symbols.len() ); } ```