Task 1:

• decodes a string encoded by xoring a string with a key that has the same size as the string;
• xors every byte from the string with the byte from the key that's situated on the same position (encoded_string ^ key = decoded_string, where encoded_string = decoded_string ^ key);
• the decoded string overwrites the encoded one.

Task 2:

• decodes a string encoded by xoring the i-th byte with the i-1-th byte, (i = 1, string_length);
• in order to decode it, the string has to be examined from the end, xoring the i-th byte with the i-1-th byte (i = string_length, 1);
• the decoded string overwrites the encoded one.

Task 3:

• decodes a string encoded by xoring a string with a key that has the same size as the string;
• the string and the key are represented in hex;
• the conversion from hex to byte is done in the following way: the corresponding values from the 2i-th byte and the 2i+1-th byte are calculated and the result is stored in the i-th byte of the string;
• xors every byte from the string with the byte from the key that's situated on the same position (encoded_string ^ key = decoded_string, where encoded_string = decoded_string ^ key);
• the decoded string overwrites the encoded one.

Task 4:

• decodes a base32 encoded string;
• 8 bytes(values) from the encoded string are processed at once;
• for every encoded value, the decoded one is computed using the convert_byte function;
• each part of every decoded value is placed accordingly in the 5 generated bytes of the decoded string;
• the decoded string overwrites the encoded one.

Task 5:

• decodes a string encoded by xoring every byte from a string with a one byte key;
• computes every one byte key (numbers from 0 to 255);
• for every generated key, the decoded string is generated and if the string contains the substring "force", then the key has been found, otherwise the xor operation is undone;
• the decoded string overwrites the encoded one;
• the key is returned in the eax register.

Task 6:

• decodes a string encoded using the Vigenere Cipher;
• for every byte from the encoded string (only the alphabetical characters), the offset from the letter "a" given by the corresponding byte from the key is calculated;
• the letter is shifted left (ex: byte_from_key = d, encoded_byte = c, decoded_byte = z) with the calculated offset;
• the decoded string overwrites the encoded one.