Here we propose a new block cipher called Raiden. This new cipher has been developed following a Feistel Network structure by means of genetic programming. Our intention now consists on getting as much feedback as possible from users, so we encourage you to test the algorithm and send us your opinion. We would also like to receive enhancements and new versions of the algorithm, developed in other source languages and platforms.
Our idea on developing this cipher is to propose it as an alternative to TEA block cipher. TEA is a very interesting cipher with lots of real applications. It is very simple and fast, and it reaches an acceptable level of security by the application of a lot of cycles.
Nowadays TEA has been broken, and several weaknesses of the algorithm have been discovered. Since most of these weaknesses are related to its Key Shedule routine, the authors, Roger Needham and David Wheeler proposed an extended version of the algorithm with a more complex one. This new version, which they called XTEA, did not have the expected success of its antecessor, in part because it is slower.
The algorithm known weaknesses, as well as its popularity, have made us to think it was the time to develop an alternative to TEA. This alternative, presented in this page, must have the next features:
Raiden is a very small and compact cipher. It works with blocks of 64 bits and keys of 128. As it can be seen below, the algorithm has the same main structure as TEA: it is structured in cycles, where one cycle contains two feistel rounds, and for both of them, the same round key is used. In each round, the output of the round function on a sub block is used to feed the other one. The round function of the algorithm has the same size as TEA's one, but, as commented in section Raiden Strength, it is stronger.
The Key Schedule routine is more complex than TEA's, but it is simple enough to not overload the cipher execution time. To maximize the entropy introduced by this function, in each round, its output feeds the position i%4 of the key array. This makes the key array passed to the function to evolve as the algorithm is executed, and thus generating new round keys for each cycle with that 128 bit array. This also makes that function to behave much as a prng. After analyzing the algorithm, as commented in section Results of statistical tests on Raiden with the main statistical batteries, we propose the execution of sixteen cycles. Below, the code of Raiden encoding routine is shown.
void raiden(unsigned long *data,unsigned long *result,unsigned long *key)
{
unsigned long b0=data[0], b1=data[1],i,k[4]={key[0],key[1],key[2],key[3]}, sk;
for(i=0; i< 16; i++)
{
sk=k[i%4]=((k[0]+k[1])+((k[2]+k[3])^(k[0]<<k[2])));
b0 +=((sk+b1)<<9)^((sk-b1)^((sk+b1)>>14));
b1 +=((sk+b0)<<9)^((sk-b0)^((sk+b0)>>14));
}
result[0]=b0;
result[1]=b1;
}
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The cipher receives the plain text in 'data' parameter, and puts the cipher text in the 'result'. Key contains the 128 bit cipher key.
As said before, the cipher follows a Feistel structure, so the decoding is made in the same way than the encoding but applying the round keys in the inverse order. This is the Raiden decoding routine.
void decode_raiden(unsigned long *data,unsigned long *result,unsigned long *key)
{
unsigned long b0=data[0], b1=data[1],i,k[4]={key[0],key[1],key[2],key[3]},
subkeys[16];
for(i=0;i< 16;i++){
//Subkeys are calculated
k[i%4]=((k[0]+k[1])+((k[2]+k[3])^(k[0]<<k[2])));
subkeys[i]=k[i%4];
}
for(i=15; i!=-1; i--)
{
//Process is applied in the inverse order
b1 -= ((subkeys[i]+b0)<<9)^((subkeys[i]-b0)^((subkeys[i]+b0)>>14));
b0 -= ((subkeys[i]+b1)<<9)^((subkeys[i]-b1)^((subkeys[i]+b1)>>14));
}
result[0]=b0;
result[1]=b1;
}
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In this case, the function receives the ciphertext in the 'data' parameter and puts the plain text in the 'result'. The round keys are calculated at the beginning of the function, and then they are applied in the inverse order as they were when ciphering.
The algorithm has been developed in C source code under Linux, but it can be used also in Windows. We propose you to develop new versions of it, using other programming languages and platforms.
UpThe main weaknesses of TEA, such as the Related Key Cryptanalysis, or the equivalent keys, are related with its Key Shedule routine. Thus, one of the main objectives when developing this new cipher has been to develop an stronger Key Shedule function than TEA's.
The function developed is also very simple, but not as much as TEA's. TEA Key Shedule function consists only on adding a constant (0x9e3779b9) to a variable. Thus, it is very simple to, knowing the round key of cycle i, obtain the keys corresponding to the previous and the following cycles. This is not the case in our algorithm, in which doing so it is not a trivial problem.
Therefore, the Key Shedule function behaves more as a Hash Function or pseudorandom number generator onte, and does not have the same weaknesses as TEA Key Schedule. Raiden's Round Function provided much better results in the statistical tests than TEA's one, so we can conclude it is also stronger, and, therefore, that the whole algorithm is also stronger.
When we analyzed the algorithm using the statistical tests ENT, Diehard, NIST and Sexton, we realized that Raiden results when applied 16 cycles were, in many ocassions better, and at least comparable, to TEA results when applied 32. This made us to conclude Raiden is stronger than TEA and that 16 cycles would be an enough security margin for the algorithm to be applied. The mentioned results can be consulted in the Results of statistical tests on Raiden section.
UpAs said in the introduction section, one of the main goals when proposing an alternative to TEA cipher is to be as quick as it. The next table shows the execution times measured in miliseconds of Raiden and TEA for the correspondent number of cycles.
| Cycles | Raiden | TEA |
| 8 | 1,29 | 1,07 |
| 16 | 1,54 | 1,24 |
| 32 | 1,93 | 1,53 |
Raiden cipher is a bit slower per cycle. The reason is that Raiden's Key Schedule function is bigger than TEA's. But, since Raiden applied 16 cycles is as strong as TEA applied 32, the time goal is achieved because, as it can be seen in the table, Raiden execution time for 16 cycles is equal to TEA execution time for 32. Therefore, our cipher is as fast as TEA, and better from the point of view it needs less cycles than TEA to achieve the same level of performance.
UpWe have analyzed Raiden using the main statistical batteries, such as ENT, Diehard, NIST and Sexton.Below there are several links which will direct you to the correspondent results.
As shown in the documents referred by the links placed above, Raiden passes all the batteries.
UpThis block cipher has been developed by:
'a' stands for the @ symbol.
For any comment, recommendation, enhancement or new version of the algorithm, please use the methods placed in the sourceforge.net site of Raiden:
http://sourceforge.net/projects/raiden-cipher
Do not doubt to use the algorithm and send us your feedback!
