feat: Base64 Encoding/Decoding, type: Ciphers (#1471)

* updating DIRECTORY.md

* Feat: Base64 Encoding Decoding, Type: cipher

* Feat: Base64 Encoding Decoding, Type: cipher-2

* Type checks

* updating DIRECTORY.md

* Wrong param explaination

* Namespace and comments

* Update ciphers/base64_encoding.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update ciphers/base64_encoding.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: David Leal <halfpacho@gmail.com>

DIRECTORY.md

@@ -14,6 +14,7 @@
   * [Hamming Distance](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/bit_manipulation/hamming_distance.cpp)
 
 ## Ciphers
+  * [Base64 Encoding](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/ciphers/base64_encoding.cpp)
   * [Caesar Cipher](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/ciphers/caesar_cipher.cpp)
   * [Hill Cipher](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/ciphers/hill_cipher.cpp)
   * [Morse Code](https://github.com/TheAlgorithms/C-Plus-Plus/blob/master/ciphers/morse_code.cpp)

ciphers/base64_encoding.cpp

@@ -0,0 +1,200 @@
+/**
+ * @brief [Base64 Encoding and
+ * Decoding](https://en.wikipedia.org/wiki/Base64)
+ * @details In programming, [Base64](https://en.wikipedia.org/wiki/Base64) is a
+ * group of binary-to-text encoding schemes that represent binary data (more
+ * specifically, a sequence of 8-bit bytes) in an ASCII string format by
+ * translating the data into a radix-64 representation. The term Base64
+ * originates from a specific MIME content transfer encoding. Each non-final
+ * Base64 digit represents exactly 6 bits of data. Three 8-bit bytes (i.e., a
+ * total of 24 bits) can therefore be represented by four 6-bit Base64
+ * digits.
+ * @author [Ashish Daulatabad](https://github.com/AshishYUO)
+ */
+#include <array>     /// for `std::array`
+#include <cassert>   /// for `assert` operations
+#include <iostream>  /// for IO operations
+
+/**
+ * @namespace ciphers
+ * @brief Cipher algorithms
+ */
+namespace ciphers {
+/**
+ * @namespace base64_encoding
+ * @brief Functions for [Base64 Encoding and
+ * Decoding](https://en.wikipedia.org/wiki/Base64) implementation.
+ */
+namespace base64_encoding {
+// chars denoting the format for encoding and decoding array.
+// This array is already decided by
+// [RFC4648](https://tools.ietf.org/html/rfc4648#section-4) standard
+const std::string chars =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+/**
+ * @brief Base64 Encoder
+ * @details Converts the given string to Base64 equivalent.
+ * @param input Input as a string
+ * @returns Base64 encoded string
+ */
+std::string base64_encode(const std::string &input) {
+    std::string base64_string;  /// Output of this function: base64 string
+    // base64 deals with 6-bit chars encoded as per chars, so
+    // we will always filter 6-bits from input.
+    for (uint32_t i = 0; i < input.size(); i += 3) {
+        char first_byte = input[i];  /// First byte of the iteration
+        // Take first six bits of first character.
+        // Encode the first six bits with character defined in string `chars`
+        base64_string.push_back(chars[first_byte >> 2]);
+
+        if (i + 1 < input.size()) {
+            char second_byte = input[i + 1];  /// Second byte of the iteration
+            // Take remaining two bits of first character, and four first bits
+            // from second character Combine two numbers as 6-bit digits and
+            // encode by array chars (first two bits of first byte and next four
+            // of second byte)
+            base64_string.push_back(
+                chars[(((first_byte & 3) << 4) | ((second_byte & 0xF0) >> 4))]);
+
+            if (i + 2 < input.size()) {
+                char third_byte = input[i + 2];  /// Third byte of the iteration
+                // Take remaining four bits of second character, and first two
+                // bits from third character Combine two numbers as 6-bit digits
+                // and encode by array chars (remaining four bits of second byte
+                // and first two of third byte)
+                base64_string.push_back(chars[((third_byte & 0xC0) >> 6) |
+                                              ((second_byte & 0x0F) << 2)]);
+                // Encode remaining 6-bit of third byte by array chars
+                base64_string.push_back(chars[(third_byte & 0x3F)]);
+            } else {
+                // Take remaining four bits of second character as 6-bit number
+                base64_string.push_back(chars[((second_byte & 0x0F) << 2)]);
+                base64_string.push_back('=');  // padding characters
+            }
+        } else {
+            // Take remaining two bits of first character as 6-bit number
+            base64_string.push_back(chars[((first_byte & 3) << 4)]);
+            base64_string.push_back('=');  // padding characters
+            base64_string.push_back('=');  // padding characters
+        }
+    }
+    return base64_string;
+}
+/**
+ * @brief Utility function for finding index
+ * @details Utility function for finding the position of a character in array
+ * `chars`
+ * @param c character to search in array `chars`
+ * @returns integer denoting position of character in array `chars`
+ */
+uint8_t find_idx(const char c) {
+    if (c >= 'A' && c <= 'Z') {
+        return c - 'A';
+    } else if (c >= 'a' && c <= 'z') {
+        return c - 'a' + 26;
+    } else if (c >= '0' && c <= '9') {
+        return c - '0' + 52;
+    } else if (c == '+') {
+        return 62;
+    } else if (c == '/') {
+        return 63;
+    }
+    return -1;
+}
+/**
+ * @brief Base64 Decoder
+ * @details Decodes the Base64 string
+ * @param base64_str Input as a Base64 string
+ * @returns Base64 decoded string
+ */
+std::string base64_decode(const std::string &base64_str) {
+    std::string
+        base64_decoded;  /// Output of this function: base64 decoded string
+    for (uint32_t i = 0; i < base64_str.size(); i += 4) {
+        /// First 6-bit representation of Base64
+        char first_byte = base64_str[i];
+        /// Second 6-bit representation of Base64
+        char second_byte = base64_str[i + 1];
+        // Actual str characters are of 8 bits (or 1 byte):
+        // :: 8 bits are decode by taking 6 bits from 1st byte of base64 string
+        // and first 2 bits from 2nd byte of base64 string.
+        char first_actual_byte = static_cast<char>(
+            (find_idx(first_byte) << 2) | ((find_idx(second_byte)) >> 4));
+        base64_decoded.push_back(first_actual_byte);
+        if (i + 2 < base64_str.size() && base64_str[i + 2] != '=') {
+            /// Third 6-bit representation of Base64
+            char third_byte = base64_str[i + 2];
+            // :: Next 8 bits are decode by taking remaining 4 bits from 2nd
+            // byte of base64 string and first 4 bits from 3rd byte of base64
+            // string.
+            char second_actual_byte =
+                static_cast<char>(((find_idx(second_byte) & 0x0F) << 4) |
+                                  (find_idx(third_byte) >> 2));
+            base64_decoded.push_back(second_actual_byte);
+
+            if (i + 3 < base64_str.size() && base64_str[i + 3] != '=') {
+                /// Fourth 6-bit representation of Base64 string
+                char fourth_byte = base64_str[i + 3];
+                // :: Taking remaining 2 bits from 3rd byte of base64 string
+                // and all 6 bits from 4th byte of base64 string.
+                char third_actual_byte =
+                    static_cast<char>(((find_idx(third_byte) & 0x03) << 6) |
+                                      find_idx(fourth_byte));
+                base64_decoded.push_back(third_actual_byte);
+            }
+        }
+    }
+    return base64_decoded;
+}
+}  // namespace base64_encoding
+}  // namespace ciphers
+
+/**
+ * @brief Self test-implementations
+ * @returns void
+ */
+static void test() {
+    // 1st Test
+    std::string str =
+        "To err is human, but to really foul things up you need a computer.";
+    std::string base64_str = ciphers::base64_encoding::base64_encode(str);
+    std::string verify =
+        "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZW"
+        "VkIGEgY29tcHV0ZXIu";
+    // verify encoding
+    assert(base64_str == verify);
+    std::string original_str =
+        ciphers::base64_encoding::base64_decode(base64_str);
+    // verify decoding
+    assert(original_str == str);
+
+    // 2nd Test from [Wikipedia](https://en.wikipedia.org/wiki/Base64)
+    str =
+        "Man is distinguished, not only by his reason, but by this singular "
+        "passion from other animals, which is a lust of the mind, that by a "
+        "perseverance of delight in the continued and indefatigable generation "
+        "of knowledge, exceeds the short vehemence of any carnal pleasure.";
+
+    base64_str = ciphers::base64_encoding::base64_encode(str);
+    verify =
+        "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieS"
+        "B0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBh"
+        "IGx1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodC"
+        "BpbiB0aGUgY29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25v"
+        "d2xlZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbG"
+        "Vhc3VyZS4=";
+    // verify encoding
+    assert(base64_str == verify);
+    original_str = ciphers::base64_encoding::base64_decode(base64_str);
+    // verify decoding
+    assert(original_str == str);
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main() {
+    test();  // run self-test implementations
+    return 0;
+}