TRANSPOSITION TECHNIQUE

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TRANSPOSITION TECHNIQUE Kriptografi - Week 5

Aisyatul Karima, 2012

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Standar Kompetensi  Pada akhir semester, mahasiswa menguasai pengetahuan, pengertian, & pemahaman tentang teknik-teknik kriptografi. Selain itu mahasiswa diharapkan mampu mengimplementasikan salah satu teknik kriptografi untuk mengamankan informasi yang akan dikirimkan melalui jaringan.

Kompetensi Dasar      

Mahasiswa menguasai teknik transposisi Mahasiswa mampu menyelesaikan soal transposisi rail fence Mahasiswa mampu menyelesaikan soal transposisi route Mahasiswa mampu menyelesaikan soal transposisi kolom Mahasiswa mampu menyelesaikan soal transposisi ganda Mahasiswa mampu menyelesaikan soal transposisi myszkowski

Contents 1

Transposition Technique

2

Rail Fence Transposition

3

Route Transposition

5

Column Transposition

6

Double Transposition

7

Myszkowski Transposition

Transposition Method

 Transposition method is the encryption method with exchange the location of plaintext.  Returning the location of message based on the key and the transposition algorithm to decrypt the ciphertext.

Transposition Method

 There are the transposition algorithm :     

Rail Fence Transposition Route Transposition Column Transposition Double Transposition Myszkowski Transposition


 Rail Fence is transposition encoding with writing the letter of plaintext by starting from top down and then up to top on imaginary fence  The encode text read row by row.


 Example :  Plaintext : TENTUKAN PRIORITAS ANDA SEBAB KITA TIDAK DAPAT MENGERJAKAN SEMUANYA X.

 Algorithm : 5 rows  Encoding process : T–-–-–-–P–-–-–-–S–-–-–-–-A–-–- E–- –- –N– R–- –- –A–A–- –- –B– B– --–N–-–A–-–I–-–T–-–N–-–E–-–K–-–-T–K–-–-–O–I–-–-–D–S–-–-–I- – - – U – - – - – - – R – - – - – - – A – - – - – - – T – DST

 Define the Ciphertext : …. ???

Route Transposition  Transposition encoding with the route method same with the Rail Fence.  Route Transposition encoding by writing the plaintext in column top to bottom in an imaginary lattice with the size has been agreed.  The message read with route according to the agreement, example :    

Read by clockwise spiral Start from top left snakes and ladders Start from bottom right, etc.

Route Transposition  Route encoding has many algorithm to read the message.  But, not all these algorithm produce the secure cipher text.  Many algorithm do not random the plaintext perfectly, so give the gap for the cryptanalyst.  The popular route transposition is Union Route that used by US’s army on war.

Route Transposition


 Algorithm : 5 rows, spiral turning clockwise starting from top left

 Encoding process : T K I AA B T D M R N A EAO SS K IAE JS N N N RAEI D PNAEY T P I N B TAAG K M A U R T D AA K T E A U X

 Ciphertext : …. ???


 Column Transposition encoding write row by row with the same length key.  The ciphertext read column by column randomly through the number key permutation.  The row length and column permutation called by “key”.


 In encryption process, the key must be converted into the number as the sequence alphabet.  In decryption process, use the same step.

Column Transposition  Example :  Plaintext : TENTUKAN PRIORITAS ANDA SEBAB KITA TIDAK DAPAT MENGERJAKAN SEMUANYA X.

 Key : PENTING means 7 columns  Encoding process : PENTING defined as the sequence alphabet become : 6 1 4 7 3 5 2 T E N T U K A N P R I O R I T A S A N D A S E B A B K I T A T

I D A K

D A P A T M E N G E R J A K A N S E M U A N Y A X

P E N T I

N G

6 1 4 7 3 5 2


 Double transposition encoding is the column encryption method that done by twice encryption.  Twice the encoding process is done to make difficult decrypt the column transposition plaintext.  The second encoding process can use the same key or the different key.

Double Transposition  Example :  Define the second different key is GERHANA; based on the fisrt ciphertext : EPAEA AGNYA IAIKE KAUON BDTJM NRSBT PESAK RDKAM AUTNT STDNA NTIAA IAREX

 Encoding process : GERHANA defined as sequencial alphabet become : 4 3 7 5 1 6 2 4 3 7 5 1 6 2 E P A E A A G N Y A

I A I K

E K A U O N B D T J M N R S B T P E S A K R D K A M A U T N T S T D N A N T

I A A I

A R E X


 On world war I and II, the double transposition encryption used by the nation as the encoding process for the secure message.


 On 1902 Émile Victor Théodore Myszkowski has been introduced the variant of column transposition encoding, which are distinguished in the definition and permutation keywords.  On column transposition encoding, the key is BOROBUDUR that defined become 1 4 6 5 2 8 3 9 7;  But, on Myszkowski method, the key become 134315254


 The ciphertext read by the sequence number column, if there is the same sequnce number column, read simultaneously starting from the left.  Transposition method combined with the substitution method to make difficult the cryptanalyst.



 Key : BOROBUDUR means 9 column  Encoding process : BOROBUDUR defined as sequence alphabet become : 1 3 4 3 1 5 2 5 4 1 3 4 3 1 5 2 5 4 T E N T U K A N P R I O R I T A S A N D A S E B A B K I T A T I D A K D A P A T M E N G E R J A K A N S E M U A N Y A X

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TRANSPOSITION TECHNIQUE

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