Red Pike cipher
Cathal Garvey
cathalgarvey at cathalgarvey.me
Fri Feb 28 01:51:34 PST 2014
Was it not in vogue during Crypto Wars 1.0 to promulgate ciphers with a
keystrength that was feasible for big-crypto to smash but not the peasantry?
If I'm reading you correctly, this cipher has less than 64 bits of
security, more than DES at time of release. But, were attacks on this
type of cipher known at the time it was written, which could be used to
lower the effective strength for those "in the know"?
Of course now I'd expect that a look around would find plenty of attacks
on this cipher family. I'm just curious as to whether GCHQ were
spreading a secret cipher algorithm to which they probably already had a
set of good attacks at the time.
On 28/02/14 01:04, Alfonso De Gregorio wrote:
> Le limited information available on the Red Pike cipher are quite
> consistent with the code below: an ARX block cipher, no look-up
> tables, virtually no key schedule, and requiring only few lines of
> code [1].
>
> With a 64 bit key size the Alleged Red Pike (ARP) is insecure by
> modern standards. But it was possibly insecure also in the 1990s.
>
> ARP suffers from a large number of semi-weak keys. Actually, each key
> is a semi-weak key. A pair of ARP keys (K1, K2) is said to be
> semi-weak if E_K1(E_K2(M)) = M (i.e., encryption with K1 operates as
> does decryption with K2). With ARP Feistel structure and its key
> schedule,there are 2^63 such pairs, reducing the size of the key space
> to 2^63.
>
> The relationship between each semi-weak pairs is:
>
> K2_L = K1_R - 2^32/phi * 17
> K2_R = K1_L + 2^32/phi * 17
>
> where phi is the golden ratio.
>
> Being semi-weak keys a large fraction of the ARP key space,
> implementations cannot apply the standard countermeasures against this
> undesirable property. Picking a semi-weak key is inevitable.
>
>
> The question remains: Is the Alleged Red Pike the cipher designed by the GCHQ?
>
>
> [1] Anderson, Ross; Kuhn, Markus, "Low Cost Attacks on Tamper
> Resistant Devices", in M. Lomas et al. (ed.), Security Protocols, 5th
> International Workshop, Paris, France, April 7{9, 1997, Proceedings,
> Springer LNCS 1361, pp 125-136, ISBN 3-540-64040-1,
> http://www.cl.cam.ac.uk/~rja14/Papers/tamper2.pdf
>
>
> On Thu, Feb 27, 2014 at 1:08 PM, Anonymous Remailer (austria)
> <mixmaster at remailer.privacy.at> wrote:
>>
>> /* Red Pike cipher source code */
>>
>> #include <stdint.h>
>>
>> typedef uint32_t word;
>>
>> #define CONST 0x9E3779B9
>> #define ROUNDS 16
>>
>> #define ROTL(X, R) (((X) << ((R) & 31)) | ((X) >> (32 - ((R) & 31))))
>> #define ROTR(X, R) (((X) >> ((R) & 31)) | ((X) << (32 - ((R) & 31))))
>>
>> void encrypt(word * x, const word * k)
>> {
>> unsigned int i;
>> word rk0 = k[0];
>> word rk1 = k[1];
>>
>> for (i = 0; i < ROUNDS; i++)
>> {
>> rk0 += CONST;
>> rk1 -= CONST;
>>
>> x[0] ^= rk0;
>> x[0] += x[1];
>> x[0] = ROTL(x[0], x[1]);
>>
>> x[1] = ROTR(x[1], x[0]);
>> x[1] -= x[0];
>> x[1] ^= rk1;
>> }
>>
>> rk0 = x[0]; x[0] = x[1]; x[1] = rk0;
>> }
>>
>> void decrypt(word * x, const word * k)
>> {
>> word dk[2] =
>> {
>> k[1] - CONST * (ROUNDS + 1),
>> k[0] + CONST * (ROUNDS + 1)
>> };
>>
>> encrypt(x, dk);
>> }
>>
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