The following is an example of a real-life scenario that was recently encountered. A substitution cipher is when letters are replaced by other letters to form a new, hidden message. During a CTF that was hosted by "NullCon" we came across a challenge that looked like a substitution cipher. The challenge was:
Find the key:
TaPoGeTaBiGePoHfTmGeYbAtPtHoPoTaAuPtGeAuYbGeBiHoTaTmPtHoTmGePoAuGe ErTaBiHoAuRnTmPbGePoHfTmGeTmRaTaBiPoTmPtHoTmGeAuYbGeTbGeLuTmPtTm PbTbOsGePbTmTaLuPtGeAuYbGeAuPbErTmPbGeTaPtGePtTbPoAtPbTmGeTbPtEr GePoAuGeYbTaPtErGePoHfTmGeHoTbAtBiTmBiGeLuAuRnTmPbPtTaPtLuGePoHf TaBiGeAuPbErTmPbPdGeTbPtErGePoHfTaBiGePbTmYbTmPbBiGeTaPtGeTmTlAt TbOsGeIrTmTbBiAtPbTmGePoAuGePoHfTmGePbTmOsTbPoTaAuPtBiGeAuYbGeIr TbPtGeRhGeBiAuHoTaTbOsGeTbPtErGeHgAuOsTaPoTaHoTbOsGeRhGeTbPtErGePoAuGePoHfTmGeTmPtPoTaPbTmGeAtPtTaRnTmPbBiTmGeTbBiGeTbGeFrHfAuOs TmPd
To solve this problem, we run our string against values in our periodic dictionary and transformed the discovered values into their ascii form. This in returned the output of our final answer:
string = "TaPoGeTaBiGePoHfTmGeYbAtPtHoPoTaAuPtGeAuYbGeBiHoTaTmPtHoTmGePoA uGeErTaBiHoAuRnTmPbGePoHfTmGeTmRaTaBiPoTmPtHoTmGeAuYbGeTbGeLuTmP tTmPbTbOsGePbTmTaLuPtGeAuYbGeAuPbErTmPbGeTaPtGePtTbPoAtPbTmGeTbP tErGePoAuGeYbTaPtErGePoHfTmGeHoTbAtBiTmBiGeLuAuRnTmPbPtTaPtLuGeP oHfTaBiGeAuPbErTmPbPdGeTbPtErGePoHfTaBiGePbTmYbTmPbBiGeTaPtGeTmT lAtTbOsGeIrTmTbBiAtPbTmGePoAuGePoHfTmGePbTmOsTbPoTaAuPtBiGeAuYbG eIrTbPtGeRhGeBiAuHoTaTbOsGeTbPtErGeHgAuOsTaPoTaHoTbOsGeRhGeTbPtE rGePoAuGePoHfTmGeTmPtPoTaPbTmGeAtPtTaRnTmPbBiTmGeTbBiGeTbGeFrHfA uOsTmPd"
n=2
list = []
answer = []
[list.append(string[i:i+n]) for i in range(0, len(string), n)]
print set(list)
periodic ={"Pb": 82, "Tl": 81, "Tb": 65, "Ta": 73, "Po": 84, "Ge": 32, "Bi": 83, "Hf": 72, "Tm": 69, "Yb": 70, "At": 85, "Pt": 78, "Ho": 67, "Au": 79, "Er": 68, "Rn": 86, "Ra": 88, "Lu": 71, "Os": 76, "Tl": 81, "Pd": 46, "Rh": 45, "Fr": 87, "Hg": 80, "Ir": 77}
for value in list:
if value in periodic:
answer.append(chr(periodic[value]))
lastanswer = ''.join(answer)
print lastanswerTo start this script off, we first defined the key string within the script. The n variable was then defined as 2 for later use and two empty lists were created— list and answer:
string = --snipped-- n=2 list = [] answer = []
We then started to create the list, which ran through the string and pulled out the sets of two letters and appended them to the list value, which was then printed:
[list.append(string[i:i+n]) for i in range(0, len(string), n)] print set(list)
Each of the two letters corresponded to a value in the periodic table, which relates to a number. Those numbers when transformed into ascii related to a character. Once this was discovered, we needed to map the elements to their periodic number and store that:
periodic ={"Pb": 82, "Tl": 81, "Tb": 65, "Ta": 73, "Po": 84, "Ge": 32, "Bi": 83, "Hf": 72, "Tm": 69, "Yb": 70, "At": 85, "Pt": 78, "Ho": 67, "Au": 79, "Er": 68, "Rn": 86, "Ra": 88, "Lu": 71, "Os": 76, "Tl": 81, "Pd": 46, "Rh": 45, "Fr": 87, "Hg": 80, "Ir": 77}We are then able to create a loop that will go through the list of elements that we previously created and named as list, and map them to the value in the periodic set of data that we created. As this is running, we can have it append the findings into our answer string while transforming the ascii number to the relevant letter:
for value in list:
if value in periodic:
answer.append(chr(periodic[value]))Finally, we need to have the data printed to us:
lastanswer = ''.join(answer) print lastanswer
Here is an example of the script running:
set(['Pt', 'Pb', 'Tl', 'Lu', 'Ra', 'Pd', 'Rn', 'Rh', 'Po', 'Ta', 'Fr', 'Tb', 'Yb', 'Bi', 'Ho', 'Hf', 'Hg', 'Os', 'Ir', 'Ge', 'Tm', 'Au', 'At', 'Er']) IT IS THE FUNCTION OF SCIENCE TO DISCOVER THE EXISTENCE OF A GENERAL REIGN OF ORDER IN NATURE AND TO FIND THE CAUSES GOVERNING THIS ORDER. AND THIS REFERS IN EQUAL MEASURE TO THE RELATIONS OF MAN - SOCIAL AND POLITICAL - AND TO THE ENTIRE UNIVERSE AS A WHOLE.