Task: Bacon cipher

C: #include <stdio.h>
#include <string.h>
#include <stdlib.h>


char *codes[] = {
    "AAAAA", "AAAAB", "AAABA", "AAABB", "AABAA",
    "AABAB", "AABBA", "AABBB", "ABAAA", "ABAAB",
    "ABABA", "ABABB", "ABBAA", "ABBAB", "ABBBA",
    "ABBBB", "BAAAA", "BAAAB", "BAABA", "BAABB",
    "BABAA", "BABAB", "BABBA", "BABBB", "BBAAA",
    "BBAAB", "BBBAA"
};

char *get_code(const char c) {
    if (c >= 97 && c <= 122) return codes[c - 97];
    return codes[26];
}

char get_char(const char *code) {
    int i;
    if (!strcmp(codes[26], code)) return ' ';
    for (i = 0; i < 26; ++i) {
        if (strcmp(codes[i], code) == 0) return 97 + i;
    }
    printf("\nCode \"%s\" is invalid\n", code);
    exit(1);
}

void str_tolower(char s[]) {
    int i;
    for (i = 0; i < strlen(s); ++i) s[i] = tolower(s[i]);
}

char *bacon_encode(char plain_text[], char message[]) {
    int i, count;
    int plen = strlen(plain_text), mlen = strlen(message);
    int elen = 5 * plen;
    char c;
    char *p, *et, *mt;
    et = malloc(elen + 1);  
    str_tolower(plain_text);
    for (i = 0, p = et; i < plen; ++i, p += 5) {
        c = plain_text[i];
        strncpy(p, get_code(c), 5);
    }
    *++p = '\0';

    
    str_tolower(message);
    mt = calloc(mlen + 1, 1);
    for (i = 0, count = 0; i < mlen; ++i) {
        c = message[i];
        if (c >= 'a' && c <= 'z') {
            if (et[count] == 'A')
                mt[i] = c;
            else
                mt[i] = c - 32;  
            if (++count == elen) break;
        }
        else mt[i] = c;
    }
    free(et);     
    return mt;
}

char *bacon_decode(char cipher_text[]) {
    int i, count, clen = strlen(cipher_text);
    int plen;
    char *p, *ct, *pt;
    char c, quintet[6];
    ct = calloc(clen + 1, 1);
    for (i = 0, count = 0; i < clen; ++i) {
        c = cipher_text[i];
        if (c >= 'a' && c <= 'z')
            ct[count++] = 'A';
        else if (c >= 'A' && c <= 'Z')
            ct[count++] = 'B';
    }

    plen = strlen(ct) / 5; 
    pt = malloc(plen + 1);
    for (i = 0, p = ct; i < plen; ++i, p += 5) {
        strncpy(quintet, p, 5);
        quintet[5] = '\0';
        pt[i] = get_char(quintet);
    }
    pt[plen] = '\0';
    free(ct);
    return pt;
} 

int main() {
    char plain_text[] = "the quick brown fox jumps over the lazy dog";
    char message[] = "bacon's cipher is a method of steganography created by francis bacon."
        "this task is to implement a program for encryption and decryption of "
        "plaintext using the simple alphabet of the baconian cipher or some "
        "other kind of representation of this alphabet (make anything signify anything). "
        "the baconian alphabet may optionally be extended to encode all lower "
        "case characters individually and/or adding a few punctuation characters "
        "such as the space.";
    char *cipher_text, *hidden_text;
    cipher_text = bacon_encode(plain_text, message);
    printf("Cipher text ->\n\n%s\n", cipher_text);
    hidden_text = bacon_decode(cipher_text);
    printf("\nHidden text ->\n\n%s\n", hidden_text);
    free(cipher_text);
    free(hidden_text);
    return 0;
}








VB: Imports System.Text

Module Module1

    ReadOnly CODES As New Dictionary(Of Char, String) From {
        {"a", "AAAAA"}, {"b", "AAAAB"}, {"c", "AAABA"}, {"d", "AAABB"}, {"e", "AABAA"},
        {"f", "AABAB"}, {"g", "AABBA"}, {"h", "AABBB"}, {"i", "ABAAA"}, {"j", "ABAAB"},
        {"k", "ABABA"}, {"l", "ABABB"}, {"m", "ABBAA"}, {"n", "ABBAB"}, {"o", "ABBBA"},
        {"p", "ABBBB"}, {"q", "BAAAA"}, {"r", "BAAAB"}, {"s", "BAABA"}, {"t", "BAABB"},
        {"u", "BABAA"}, {"v", "BABAB"}, {"w", "BABBA"}, {"x", "BABBB"}, {"y", "BBAAA"},
        {"z", "BBAAB"}, {" ", "BBBAA"} 
    }

    Function Encode(plainText As String, message As String) As String
        Dim pt = plainText.ToLower()
        Dim sb As New StringBuilder()
        For Each c In pt
            If "a" <= c AndAlso c <= "z" Then
                sb.Append(CODES(c))
            Else
                sb.Append(CODES(" "))
            End If
        Next

        Dim et = sb.ToString()
        Dim mg = message.ToLower() 

        sb.Length = 0
        Dim count = 0
        For Each c In mg
            If "a" <= c AndAlso c <= "z" Then
                If et(count) = "A" Then
                    sb.Append(c)
                Else
                    sb.Append(Chr(Asc(c) - 32)) 
                End If
                count += 1
                If count = et.Length Then
                    Exit For
                End If
            Else
                sb.Append(c)
            End If
        Next

        Return sb.ToString()
    End Function

    Function Decode(message As String) As String
        Dim sb As New StringBuilder

        For Each c In message
            If "a" <= c AndAlso c <= "z" Then
                sb.Append("A")
            ElseIf "A" <= c AndAlso c <= "Z" Then
                sb.Append("B")
            End If
        Next

        Dim et = sb.ToString()
        sb.Length = 0
        For index = 0 To et.Length - 1 Step 5
            Dim quintet = et.Substring(index, 5)
            Dim key = CODES.Where(Function(a) a.Value = quintet).First().Key
            sb.Append(key)
        Next

        Return sb.ToString()
    End Function

    Sub Main()
        Dim plainText = "the quick brown fox jumps over the lazy dog"
        Dim message =
            "bacon
            "this task is to implement a program for encryption and decryption of " +
            "plaintext using the simple alphabet of the baconian cipher or some " +
            "other kind of representation of this alphabet (make anything signify anything). " +
            "the baconian alphabet may optionally be extended to encode all lower " +
            "case characters individually and/or adding a few punctuation characters " +
            "such as the space."

        Dim cipherText = Encode(plainText, message)
        Console.WriteLine("Cipher text ->" & Environment.NewLine & "{0}", cipherText)

        Dim decodedText = Decode(cipherText)
        Console.WriteLine(Environment.NewLine & "Hidden text ->" & Environment.NewLine & "{0}", decodedText)
    End Sub

End Module