132 lines
3.4 KiB
Rust
132 lines
3.4 KiB
Rust
pub const BASE64_ALPHABET : &str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=-_";
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pub const HEX_ALPHABET : &str = "ABCDEFabcdef0123456789";
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// Calculate the shannon entropy of a given byte slice
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pub fn shannon_entropy(bytes: &[u8]) -> f32 {
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let mut entropy = 0.0;
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let mut counts = [0; 256];
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for &b in bytes {
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counts[b as usize] += 1;
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}
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for &count in counts.iter() {
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if count == 0 { continue }
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let p: f32 = (count as f32) / (bytes.len() as f32);
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entropy -= p * p.log(2.0);
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}
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entropy
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}
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// Calculate the shannon entropy of a given byte slice for a specific charset
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pub fn shannon_entropy_charset(bytes: &[u8], charset: &str) -> f32 {
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let mut entropy = 0.0;
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for single_char in charset.chars() {
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let count = bytes.iter().filter(|&&n| n as char == single_char).count();
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if count == 0 { continue }
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let p: f32 = (count as f32) / (bytes.len() as f32);
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entropy -= p * p.log(2.0);
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}
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entropy
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}
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// Determine if a string is made up only of hexdigits
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pub fn is_hex_str(s: &str) -> bool {
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s.chars().filter(|&n| !(n.is_digit(16))).count() == 0
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}
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// Determine if a string is made up only of base64/base64url digits
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pub fn is_base64_str(s: &str) -> bool {
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let alphabet: Vec<_> = BASE64_ALPHABET.chars().collect();
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s.chars().filter(|n| !(alphabet.contains(n))).count() == 0
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}
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// Calculate the shannon entropy of a given string
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pub fn str_entropy(s: &str) -> f32 {
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if is_hex_str(s) {
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return shannon_entropy_charset(s.as_bytes(), HEX_ALPHABET);
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}
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if is_base64_str(s) {
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return shannon_entropy_charset(s.as_bytes(), BASE64_ALPHABET);
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}
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shannon_entropy(s.as_bytes())
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}
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// Tests
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#[cfg(test)]
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mod tests {
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use super::{shannon_entropy, str_entropy, is_hex_str, is_base64_str};
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#[test]
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fn test_entropy() {
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let test_strings = vec![
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("hello world", 2.8453512),
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("hello worldd", 2.8553884),
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("a", 0.0),
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("aaaaa", 0.0),
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("ab", 1.0),
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("aab", 0.9182958),
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("", 0.0),
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];
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for (test, answer) in test_strings {
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let entropy: f32 = str_entropy(test);
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assert_eq!(entropy, answer);
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}
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}
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#[test]
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fn test_entropy_equal_distribution1() {
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let mut bytes = [0u8; 256];
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for i in 0..256 {
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bytes[i] = i as u8;
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}
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let h = shannon_entropy(&bytes);
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assert_eq!(h, 8.0);
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}
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#[test]
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fn test_entropy_equal_distribution2() {
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let mut bytes = [0u8; 256*2];
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for i in 0..bytes.len() {
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bytes[i] = (i % 256) as u8;
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}
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let h = shannon_entropy(&bytes);
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assert_eq!(h, 8.0);
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}
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#[test]
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fn test_entropy_helloworld() {
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let h = str_entropy("hello, world");
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assert_eq!(h, 3.0220551);
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let h = str_entropy("hello world");
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assert_eq!(h, 2.8453512);
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}
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#[test]
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fn test_hex_str_reconizer() {
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let s = is_hex_str("0123456789abcdef0123456789abcdef");
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assert_eq!(s, true);
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let s = is_hex_str("68656c6c6f20776f726c64");
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assert_eq!(s, true);
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let s = is_hex_str("g");
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assert_eq!(s, false);
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}
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#[test]
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fn test_base64_str_reconizer() {
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let s = is_base64_str("aGVsbG8gd29ybGQ=");
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assert_eq!(s, true);
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let s = is_base64_str("#@$");
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assert_eq!(s, false);
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}
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}
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