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## 12/4/13

### Sample Cipher using Stitie Space.

To create 'public' key of a pair, proceed as follows:

1. Divide n-bit blocks into k-bit blocks, where k<n.
2. Select up to n2 k-bit common input blocks, where n is cryptographic security level of cipher and k<n and k divides n (it's not ideal cipher, just one of key pairs under it).If n2 > 2k then use 2k common input blocks.
3. Select large prime numbers (equal amount to selected k-bit blocks in point 2), call them 'pn1', 'pn2', ... . They should not be sequential, and each of key pairs should have different sets.
4. Assign primes selected above to the common input blocks selected above.
5. Prepare beginning protocol of a cipher, selected or randomly chosen but remembered bits to use in first block(s) of ciphertext. This is secret shared by 'private' and 'public' key pair. Different key pairs have different bits.
6. Select minimum and maximum threshold of common k-bit blocks or their concatenations considered. For each selected common k-bit block or concatenation, precalculate a number, a product of primes assigned to selected common k-bit blocks. Assign a 'reserved' block to each of them.
7. Prepare functions, complex or not, and assign them to prime products computed above.
8. Prepare ending protocol of a cipher, mentioning which common input blocks should be processed differently. These are blocks bitwise equal to 'reserved' blocks assigned to products of primes mentioned above.
9. Whole ciphertext, including beginning and ending protocols should be malformed so it's hard to guess them easily. Develop such methods for each of key pairs independently.

This key can be used as follows:

1. Create beginning protocol block(s) of a cipher as designed above.
2. Add all values that belong to ending protocol there, and insert it in selected place (any place in the ciphertext to be processed, after the beginning protocol).

repeat in rounds (as many times for each block as neccessary):

3. For each concatentation of selected common k-bit input blocks in n-bit block (according to selected minimum and maximum concatenations threshold), substitute it for 'reserved' block, assigned to a product of primes.
4. For rest of k-bit input blocks in n-bit block, transform them somehow, with functions, complex or not, selected depending on last product of primes before that block. These functions are a secret of this 'public' key.
5. If this is first n-bit block, XOR beginning protocol with beginning n-bit block(s) before proceeding onward, but only once, not per round.
6. If this is not first n-bit block, XOR it with previous block.

end of repeat in rounds.

7. Malform whole ciphertext somehow.

To create 'private' key of a pair, proceed as follows:

1. Add 'public' key secrets to the 'private' key.
2. Add properly indexed primes and products to the 'private' key.
3. Add reversed functions to the 'private' key.

This key can be used as follows:

Reverse order of operations then decipher using reversed functions, accounting for beginning and ending protocol. Proceed from first block of ciphertext to last. Because we know all secrets, we can proceed fast without need to guess through trapdoor function, which is time-wise costly.

This key pair can be generated by Stitie Space, as mentioned few posts earlier, with few improvements.

Succesful use of this cipher depends on amount and size of prime numbers at users disposal (and opponent's).

Public key files should be encrypted, signed and certified. Software for encryption using such keys should not be open-source, and it's binary executable should be obfuscated. To protect secrets of public keys and its ciphers.

Critic is welcome and requested.

1. Such ciphers can be combined with AES (Advanced Encryption Standard), for example by putting them in S-Boxes, wrapping if neccessary with modulo operation.

2. 'wrapping' can be understood as: using last k-bits of ciphertext as S-Box output.

3. more precisely, last k-bits of such ciphertext can be XOR-ed with input in S-Box to produce output.