task 1: frequency analysis against monoalphabetic substitution cipher

After altering the bit the decryption process is performed, and it is observed that no changes have endstream For instance, we see that now we have at least one occurrence of every letter. /Filter /FlateDecode /BBox [0 0 100 100]

Here we see a veritable ocean of seemingly obvious mappings with few, if any, significant outliers. /FormType 1 Two are pretty clear but in even these are not grouped too tightly. x���P(�� �� 54 0 obj /Subtype /Form It's time to see if we can leverage what we've learnt in recent lessons and crack a monoalphabetic cipher. Nonetheless they maybe helpful in breaking ties, at least tentatively in our mappings based on single character frequencies. And if that doesn't work, well then we need to back out a little bit and try grouping larger groups. Demand for cybersecurity jobs is expected to rise 6 million globally by 2019, with a projected shortfall of 1.5 million, according to Symantec, the world’s largest security software vendor. The pairings shown are simply my best estimate, and we'll keep in mind that these are probably some of the first mappings that we should consider playing around with later on if it appears we haven't quite cracked the cipher. W~�� S�ƅ@���ק�y")�;k���۷��!Ɩh0��-���,b��!��I^ĥ���OԿ�P �my�n7�*�����,�E�����%�� ʪ��p� gƞ]�Vk�"F�X����po \�,��/������p�N"!6�mc$�p��޳�qaj;��������4@J����X���nY �7�G���5\9�q�~R�_�On,5�ب4���"�]�NZZ@�5��vr���}3�s�����Y�w#3ޥ�_bKL����{�Bw1�0�������MRh�-}�A"�v)*�s��]�߳�Q�r���*���O&@@�I��ѓiӽ��v2�y $�x?A4�,54^UKG�W��y.������3��`?�W(��P� �[�W�7�+Q�SI�y�{�����i*�=3psn�{r@��s�S�۫��u��S� �`��H�M����9P�~ ��!6Ƶ؂����l ��O�� Ա���9H�N9#�.��Uvp��EN��ie֪�G�!c��!��ʖ#��_�O�{}B�������׸�V���Z���gY����y��-�'���27�� �.ws���v7�#�V�y�*:s�U��c�wM��� ��a�\u6�Zi�n��� ~�!A�+%"��VGDxn�(��f!��" `�Đ�/(��f*��eF��qi �]k*2~�������!rlp�C�@��ç� For cbc encrypted image we have also replaced first 54 bits in order to make it viewable. In this case I've chosen to just map them as show, since this results in a overall lower error. /Resources 36 0 R What this cipher does is, as its name suggests, to simply substitute each character in the message with the character it is mapped to. Set the step size to 1… ���lp�PU�(ʡ���b? Here´s what we can probably make use of the tail end of our frequency distributions. /Type /XObject Another good guess would be that either b or m represents plaintext q. /BBox [0 0 100 100] /Subtype /Form stream

stream I tend to think it was the latter giving the kind of highly skilled and practice cryptanalyst at. �#�ƍ�#����� ��� P�4=^c�p8�O �%�[V��)@h8�8�SX�����v�"�|l�G�? And if it does then it would be an easy matter to scan the ciphertext and see if one of these two letters is virtually always followed by the same letter. The first, third, and fourth letters should be the same. endstream /Length 15 x���P(�� �� /Filter /FlateDecode ߺ�Nm�����K��ď]��ZѪ��.=��ڵ�� )�y�bQ$^�8��-BX�����o;�t0p���;����q���ߣ��h�l}i�@W��~�衃�9�A�NX�o�Y ��]�H��~钷��%�u�+ ��[w�ѝ�\��h�I0��#ĉ��0&�f��a4����ƭ���=�.�i������I�%�

The frequency analysis for this set of 2500 characters shows significantly finer grain in the results. this seed lab is about symmetric key encryption, National University of Computer and Emerging Sciences, Task 1: Frequency Analysis Against Monoalphabetic Substitution Cipher. << In fact, our least frequently recurring cyphertext letter, m, occurs 23 times.

/FormType 1 In this case, they happen to be the one we've already looked at plus another nine ciphertext that are also excerpts from Leo Tolstoy novels. But even if I'm wrong, there's only one alternative to try. But let's first go for some low hanging fruit and see what our plot of double letter versus single letter frequencies suggests. /BBox [0 0 100 100] For digraph ciphers (Playfair, Bifid, Four-square, etc), the step size should be 2 and offset 0. >> /Length 15

Not necessarily the same one as the one we're primarily interested in, though. stream /Type /XObject 33 0 obj Next we look at the handful of characters down near the origin. endstream endobj /BBox [0 0 100 100] %PDF-1.5 �ح�!�����x�`�z����ۋ��-a�W�� M�������{w�:Q-����ǁSP/�g[g�����;U�[Hl��fL��̏\��\����,���x�1����� ���ʴ�oն.�jD����2F���T3�/��7���ZU��������wfL��Y@D���y��f��ƚ�a,�o[��&�w�����93���#�^#������Y����ǜ�8F1�2�G��������k�����^aci�ř��1��x �#J"�O*>ϗع���_�߳ ,�o�O�0Utl���T��g}0A/�Q{'s�q0B���b�û��䝶�O����!��Bj�Zlײ�M�%~���З�a&0�L��g��`�E�"��nܯ��[�Z��Vg��?���qа8Ҷ;�!��di��9�ǁ�j��K[��@< i�i+2�8�Xn�2� .�F� \�B;]+�c4����ů�����1����L���i�u�m�ّ&RN(�_ �D*�H�I���|��PB�"�ha��D��W�\$Cݨ� �6:�y�C&���9f$J�#�[l���O�"_��z�>۲�?6��>�>��t�J"",|��)�:>�B�z� i3(��=��r���������*�!aɋ�Z�ک����C���F�? /Filter /FlateDecode I chose Leo Tolstoy as the author and then download the text file versions of the novels listed in his Wikipedia bibliography. 1. << /FormType 1 After this the text is encrypted through the generated substitution code. /Length 15 I wouldn't be surprised if I got these last two backwards or if a couple of the ones in that dash circle aren't quite right. /Matrix [1 0 0 1 0 0] Thus, if "a" is encrypted to "R", then every time we see the letter "a" in the plaintext, we … � sA�lX��0�ۧx�gy���ÁҶ��VƓ�z���"�� Substitution Ciphers Frequency Analysis Tools. For the Trifid cipher, the step size should be 3 and offset 0. ����Z����d�� Iw3����\��|a~\�1DW�ޅ��%�=�^��H���,�1әs;�����сj�V��d#KG4���X���J�É&p\g)ۼQ'����vh����I��wƀo���1����TYT�e��J#��ӎ�0Td�˙~��;�h���7I�M��P-p�r�� /Length 15 11 0 obj

/Matrix [1 0 0 1 0 0] In this specialization, you will learn basic security issues in computer communications, classical cryptographic algorithms, symmetric-key cryptography, public-key cryptography, authentication, and digital signatures. Keeping in mind that reasonable amount of time to break a cipher can range from several hours to several months, depending on what's at stake. So our most frequent characters,i and o, had 23 occurrences.

endobj Thus brute force is infeasible.

You'll have to take my word that I didn't look ahead of time, I just dumped it out to a text file so that we could access it later. A monoalphabetic substitution cipher, also known as a simple substitution cipher, relies on a fixed replacement structure. When you have completed this module, you will have an appreciation of the different types of attacks and under what kinds of situations each might be applicable. /Length 15 endstream

/Length 15 Even for single-letter monoalphabetic substitution ciphers, a polygram analysis can be useful to detect common trigrams (like the). /Length 15 There were only nine total occurrences of repeated digraphs and only six distinct ones. /BBox [0 0 100 100] given in lab task document. In fact, our least frequently recurring cyphertext letter, m, occurs 23 times. Welcome to Introduction to Applied Cryptography. In my opinion, it should be less secure than substitution cipher although the key space is much much bigger (compare $64!$ to $26!$). x���P(�� �� Both the pigpen and the Caesar cipher are types of monoalphabetic cipher. '{ �-x�� IX��_��u ��B.�O���6+6����%��@��i��L��b��&L���9��� a�4�9��� 26 0 obj /FormType 1 7 0 obj stream endobj /Length 2299 << And then randomly pick a location within the middle half of the document to select the 250 character plaintext message. >> endobj To view this video please enable JavaScript, and consider upgrading to a web browser that /Length 15 Interesting historical concepts was available which made it very engaging and educating. Zooming in on the lower left portion of the graph but not all the way down to the origin, we have six clear pairings. It might appear that we have at least four obvious mappings, and perhaps we do, but consider that the ciphertext h and the plaintext e are sitting out there all by themselves. /Subtype /Form Which would give high confidence the first letter is the letter q and the letter that follows it represents u. /Length 2650 While it gives clues and hints and guides our search so that we can hopefully identify a few character mappings fairly quickly, it is still going to be a tedious and error prone process taking hours or perhaps even days and weeks, or perhaps months. /Type /XObject /Matrix [1 0 0 1 0 0] 9 0 obj /Filter /FlateDecode >> Clearly, frequency analysis works, at least as long as we have enough ciphertext to work with. Nice lectures. /Filter /FlateDecode That is, the substitution is fixed for each letter of the alphabet. 23 0 obj This lab has been tested on the pre-built Ubuntu 16.04 VM, which can be downloaded from the SEED website. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. This encryption is more susceptible to frequency analysis than original "substitution ciphers" because the frequency tables should be much more Non-uniform. 31 0 obj endstream /Type /XObject /Filter /FlateDecode

/Subtype /Form endobj xڵَ���}�B0DBV�>�M�`�k'>� v� X���Z#b(R!���ߧ�n��P�3����f��uK��gb��ͻ����=�"�D&gw�Y�fIl##��n3�4����7��2b�c�j�Y)��G�n2��n��B��;1�}�nN�������/w��x�E�Ui�VGBf� This is because with so limited amount of ciphertext, we see numerous ties in the single character frequencies as well. Nice delivery of concepts.

In this article, we will examine substitution ciphers specifically… endobj

/Filter /FlateDecode

/Length 15 endstream And more than three decades before she was beheaded in 1587. Cryptography is an essential component of cybersecurity. x���P(�� ��

Or simply due to someone spotting a few recognizable names or other wise seeing a recognizable pattern. 17 0 obj Thus we can have much more certainty that more of our pairings are correct. This knowledge was usually extremely important to successfully breaking the ciphertext since you only know that you've succeeded cracking the cipher if you can actually read the resulting plaintext. /Matrix [1 0 0 1 0 0] endstream x���P(�� �� The need to protect sensitive information and ensure the integrity of industrial control processes has placed a premium on cybersecurity skills in today’s information technology market. Though it's still likely that some of them are wrong. stream /Resources 10 0 R /Resources 12 0 R endobj /Resources 5 0 R \Gkjݍ83ZBR�A���xD�z��yX�i��Я�ع�I��@�z��$���y�#�,]G^+��v�� ¶Q/��7�׊dށ`Xd��Ѻ�k���-���8c:�#��R�9u���BN �A�F���[��r��,����Ly��|8�� �*/�U��&��G!���B�m��d �I̡�k����K�]S�h�e�fJ����� 58=F CX��B쟺dW��G����H��w�YVu�"��%�0I 1��)��ܭi�u��cL��G�,e��H'R We also see that there is only two repeated digraphs that don´t appear at least once.

endobj endobj /Subtype /Form /Type /XObject xڥ]s��=��Oyf�%�����n����_�m��w��ؼȢN���� H[r��t�b� �/ @��.��OW?�]���%��U|qw�(ĢH�8���n���^_\�DƢ��z �!r�nU�/y)���Rd�z"�u[�O�զ=�w��ݏ ,]Tq��e�y3^�*NG��뻫߯8�؂�6"�X��������?.X�T�������o�������%��/b��j���+�m��ˎV-y�O��8��$�U����閜EO���lpe� ���U�X��e�"�6Z�[��8�!�}��X���ՠ�G�QmbT�*�g��W�H���8xĽ� hM���~��ZK/Dm�Z��э}g5��U�|8��^%s��������B�/{��z��km�5�H���S�?~S�w��)=���ݨ �k\����k}[k�֞��ـ G?�ز��$_�e�E�j�&e\�1r'[$U,���L�����L�6�sS�u%�����JΪ�%yH�g�{�#T=�>ju8&Ӥ&AP�4.�iLp5J��v9+�ưИ��}O_�Ӄ�d��r ���E��0��*6Σ{l{ ���p�v�{y��X�ݞmTV�ѡ� ^��JH�$�ҊL�-�uRe�`�� �U�AKke�0Ђ����G�+��P0摊܁��K��������Z��%��A}~aL�]펪9k��A�S�x].X�f%4�d�5=xr?�*�����lT���fg�N<2ѭ��%> jK�-m3v�~yL�M�e�LY�9N� ��_+�����*_��UVḵڵ�*��S�j��u�[�v����05r�U���e�̣�eb���E��`%E�@�;��"@�V�����(�\��=X�1p�����ǁ�1^�����}r*��JV�.��>�H*��@�A�uKk'�����bb�

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