Codebreakers and Codewriters
Jelly, 57 + 32 = 89 bytes (cracked)

“¡ḟċ⁷Ḣṡ⁵ĊnɠñḂƇLƒg⁺QfȥẒṾ⁹+=?JṚWġ%Aȧ’
O‘ḅ256b¢*21%¢ḅ¢ḃ256’Ọ


Encrypted message:

EªæBsÊ$Ê³¢?r×­Q4e²?ò[Ý6


As a hex-string:

4518AAE6421973CA
9724CAB3A23F72D7
AD18855134651810
B23F1CF25BDD9036


Explanation:

O‘ḅ256b¢*21%¢ḅ¢ḃ256’Ọ
O                     convert each into codepoint
 ‘ḅ256                convert from bijective base 256 to integer
      b¢              convert from integer to base N
        *21           map each to its 21th power
           %¢         modulo N
             ḅ¢       convert to integer from base N
               ḃ256’  convert from integer to bijective base 256
                    Ọ convert each from codepoint


Where N is encoded by the string “¡ḟċ⁷Ḣṡ⁵ĊnɠñḂƇLƒg⁺QfȥẒṾ⁹+=?JṚWġ%Aȧ’, which is the number 105587021056759938494595233483151378724567978408381355454441180598980268016731.

Also, this is the RSA method with N given above and public key 21. Cracking this is equivalent to finding the two prime factors of N.