feat: add Base85 (ASCII85) cipher implementation (#1018)

Author: AliAlimohammadi

DIRECTORY.md

@@ -41,6 +41,7 @@
     * [Base16](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/base16.rs)
     * [Base32](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/base32.rs)
     * [Base64](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/base64.rs)
+    * [Base85](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/base85.rs)
     * [Blake2B](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/blake2b.rs)
     * [Caesar](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/caesar.rs)
     * [Chacha](https://github.com/TheAlgorithms/Rust/blob/master/src/ciphers/chacha.rs)

src/ciphers/base85.rs

@@ -0,0 +1,213 @@
+//! Base85 (Ascii85) encoding and decoding
+//!
+//! Ascii85 is a form of binary-to-text encoding developed by Adobe Systems.
+//! It encodes 4 bytes into 5 ASCII characters from the range 33-117 ('!' to 'u').
+//!
+//! # References
+//! - [Wikipedia: Ascii85](https://en.wikipedia.org/wiki/Ascii85)
+
+/// Converts a base-10 number to base-85 representation
+fn base10_to_85(mut d: u32) -> String {
+    if d == 0 {
+        return String::new();
+    }
+
+    let mut result = String::new();
+    while d > 0 {
+        result.push((d % 85 + 33) as u8 as char);
+        d /= 85;
+    }
+    result
+}
+
+/// Converts base-85 digits to a base-10 number
+fn base85_to_10(digits: &[u8]) -> u32 {
+    digits
+        .iter()
+        .rev()
+        .enumerate()
+        .map(|(i, &ch)| (ch as u32) * 85_u32.pow(i as u32))
+        .sum()
+}
+
+/// Encodes binary data using Base85 encoding
+///
+/// # Arguments
+/// * `data` - The binary data to encode
+///
+/// # Returns
+/// * `Vec<u8>` - The Base85 encoded data
+///
+/// # Examples
+/// ```
+/// use the_algorithms_rust::ciphers::base85_encode;
+///
+/// assert_eq!(base85_encode(b""), b"");
+/// assert_eq!(base85_encode(b"12345"), b"0etOA2#");
+/// assert_eq!(base85_encode(b"base 85"), b"@UX=h+?24");
+/// ```
+pub fn base85_encode(data: &[u8]) -> Vec<u8> {
+    if data.is_empty() {
+        return Vec::new();
+    }
+
+    // Convert input bytes to binary string
+    let mut binary_data = String::new();
+    for &byte in data {
+        use std::fmt::Write;
+        write!(&mut binary_data, "{byte:08b}").unwrap();
+    }
+
+    // Calculate padding needed to make length a multiple of 32
+    let remainder = binary_data.len() % 32;
+    let null_values = if remainder == 0 {
+        0
+    } else {
+        (32 - remainder) / 8
+    };
+
+    // Pad binary data to multiple of 32 bits
+    while !binary_data.len().is_multiple_of(32) {
+        binary_data.push('0');
+    }
+
+    // Split into 32-bit chunks and convert to base-85
+    let mut result = String::new();
+    for chunk in binary_data.as_bytes().chunks(32) {
+        let chunk_str = std::str::from_utf8(chunk).unwrap();
+        let value = u32::from_str_radix(chunk_str, 2).unwrap();
+        let mut encoded = base10_to_85(value);
+
+        // Reverse the string (as per original Python logic)
+        encoded = encoded.chars().rev().collect();
+        result.push_str(&encoded);
+    }
+
+    // Remove padding characters if necessary
+    if null_values % 4 != 0 {
+        let trim_len = result.len() - null_values;
+        result.truncate(trim_len);
+    }
+
+    result.into_bytes()
+}
+
+/// Decodes Base85 encoded data back to binary
+///
+/// # Arguments
+/// * `data` - The Base85 encoded data to decode
+///
+/// # Returns
+/// * `Vec<u8>` - The decoded binary data
+///
+/// # Examples
+/// ```
+/// use the_algorithms_rust::ciphers::base85_decode;
+///
+/// assert_eq!(base85_decode(b""), b"");
+/// assert_eq!(base85_decode(b"0etOA2#"), b"12345");
+/// assert_eq!(base85_decode(b"@UX=h+?24"), b"base 85");
+/// ```
+pub fn base85_decode(data: &[u8]) -> Vec<u8> {
+    if data.is_empty() {
+        return Vec::new();
+    }
+
+    // Calculate padding needed
+    let remainder = data.len() % 5;
+    let null_values = if remainder == 0 { 0 } else { 5 - remainder };
+
+    // Create padded data
+    let mut padded_data = data.to_vec();
+    padded_data.extend(std::iter::repeat_n(b'u', null_values));
+
+    // Process in 5-byte chunks
+    let mut results = Vec::new();
+    for chunk in padded_data.chunks(5) {
+        // Convert ASCII characters to base-85 digits
+        let b85_segment: Vec<u8> = chunk.iter().map(|&b| b - 33).collect();
+
+        // Convert base-85 to base-10
+        let value = base85_to_10(&b85_segment);
+
+        // Convert to binary string (32 bits)
+        let binary = format!("{value:032b}");
+        results.push(binary);
+    }
+
+    // Convert binary strings to characters
+    let mut char_chunks = Vec::new();
+    for binary_str in results {
+        for byte_str in binary_str.as_bytes().chunks(8) {
+            let byte_string = std::str::from_utf8(byte_str).unwrap();
+            let byte_value = u8::from_str_radix(byte_string, 2).unwrap();
+            char_chunks.push(byte_value);
+        }
+    }
+
+    // Calculate offset for trimming
+    let offset = if null_values % 5 == 0 {
+        0
+    } else {
+        -(null_values as isize)
+    };
+    let result_len = if offset < 0 {
+        (char_chunks.len() as isize + offset) as usize
+    } else {
+        char_chunks.len()
+    };
+
+    char_chunks.truncate(result_len);
+    char_chunks
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_encode_empty() {
+        assert_eq!(base85_encode(b""), b"");
+    }
+
+    #[test]
+    fn test_encode_12345() {
+        assert_eq!(base85_encode(b"12345"), b"0etOA2#");
+    }
+
+    #[test]
+    fn test_encode_base85() {
+        assert_eq!(base85_encode(b"base 85"), b"@UX=h+?24");
+    }
+
+    #[test]
+    fn test_decode_empty() {
+        assert_eq!(base85_decode(b""), b"");
+    }
+
+    #[test]
+    fn test_decode_12345() {
+        assert_eq!(base85_decode(b"0etOA2#"), b"12345");
+    }
+
+    #[test]
+    fn test_decode_base85() {
+        assert_eq!(base85_decode(b"@UX=h+?24"), b"base 85");
+    }
+
+    #[test]
+    fn test_encode_decode_roundtrip() {
+        let test_cases = vec![
+            b"Hello, World!".to_vec(),
+            b"The quick brown fox".to_vec(),
+            b"Rust".to_vec(),
+            b"a".to_vec(),
+        ];
+
+        for test_case in test_cases {
+            let encoded = base85_encode(&test_case);
+            let decoded = base85_decode(&encoded);
+            assert_eq!(decoded, test_case);
+        }
+    }
+}

src/ciphers/mod.rs

@@ -5,6 +5,7 @@ mod baconian_cipher;
 mod base16;
 mod base32;
 mod base64;
+mod base85;
 mod blake2b;
 mod caesar;
 mod chacha;
@@ -35,6 +36,7 @@ pub use self::baconian_cipher::{baconian_decode, baconian_encode};
 pub use self::base16::{base16_decode, base16_encode};
 pub use self::base32::{base32_decode, base32_encode};
 pub use self::base64::{base64_decode, base64_encode};
+pub use self::base85::{base85_decode, base85_encode};
 pub use self::blake2b::blake2b;
 pub use self::caesar::caesar;
 pub use self::chacha::chacha20;