On 1/4/07, Jeffrey Walton <[EMAIL PROTECTED]> wrote: > PSSR does not appear to be a viable solution for _hand keying_ a > Signature with Recovery (an example application would be a product > key). The ciphertext appears to be too large.
I have in the past used a modified MD5 (called MD5Quart) which only used 32 bit of the MD5 hash. I have include the diff to the real MD5 below. When I use this new hash as in CryptoPP::RabinSS< CryptoPP::PSSR, CryptoPP::MD5Quart >::Signer privateKey CryptoPP::RabinSS< CryptoPP::PSSR, CryptoPP::MD5Quart >::Verifier recover the overhead is 80 bit, which amount to 16 characters in a base-32 encoding. diff -u "md5.h" "md5quart.h" --- crypto/md5.h Mon Jun 16 12:02:30 2003 +++ crypto/md5quart.h Mon Jun 16 12:02:31 2003 @@ -1,22 +1,23 @@ -#ifndef CRYPTOPP_MD5_H -#define CRYPTOPP_MD5_H +#ifndef CRYPTOPP_MD5QUART_H +#define CRYPTOPP_MD5QUART_H #include "iterhash.h" NAMESPACE_BEGIN(CryptoPP) -//! <a href="http://www.weidai.com/scan-mirror/md.html#MD5";>MD5</a> -/*! 128 Bit Hash */ -class MD5 : public IteratedHashWithStaticTransform<word32, LittleEndian, 64, MD5> +/*! 32 bit hash */ +class MD5Quart : public IteratedHashWithStaticTransform<word32, LittleEndian, 64, MD5Quart> { public: - enum {DIGESTSIZE = 16}; - MD5() : IteratedHashWithStaticTransform<word32, LittleEndian, 64, MD5>(DIGESTSIZE) {Init();} + enum {DIGESTSIZE = 4}; + MD5Quart() : IteratedHashWithStaticTransform<word32, LittleEndian, 64, MD5Quart>(DIGESTSIZE) {Init();} static void Transform(word32 *digest, const word32 *data); - static const char * StaticAlgorithmName() {return "MD5";} + static const char * StaticAlgorithmName() {return "MD5Quart";} protected: void Init(); +private: + static word32 a, c, d; }; NAMESPACE_END diff -u "crypto/md5.cpp" "crypto/md5quart.cpp" --- crypto/md5.cpp Mon Jun 16 12:02:30 2003 +++ crypto/md5quart.cpp Mon Jun 16 12:02:30 2003 @@ -1,28 +1,32 @@ -// md5.cpp - modified by Wei Dai from Colin Plumb's public domain md5.c -// any modifications are placed in the public domain +// md5quart.cpp - modified by Jens Peter Secher +// from Wei Dai +// from Colin Plumb's public domain md5.c #include "pch.h" -#include "md5.h" +#include "md5quart.h" #include "misc.h" NAMESPACE_BEGIN(CryptoPP) -void MD5_TestInstantiations() +void MD5Quart_TestInstantiations() { - MD5 x; + MD5Quart x; } -void MD5::Init() +word32 MD5Quart::a; +word32 MD5Quart::c; +word32 MD5Quart::d; + +void MD5Quart::Init() { - m_digest[0] = 0x67452301L; - m_digest[1] = 0xefcdab89L; - m_digest[2] = 0x98badcfeL; - m_digest[3] = 0x10325476L; + a = 0x67452301L; + m_digest[0] = 0xefcdab89L; + c = 0x98badcfeL; + d = 0x10325476L; } -void MD5::Transform (word32 *digest, const word32 *in) +void MD5Quart::Transform (word32 *digest, const word32 *in) { -// #define F1(x, y, z) (x & y | ~x & z) #define F1(x, y, z) (z ^ (x & (y ^ z))) #define F2(x, y, z) F1(z, x, y) #define F3(x, y, z) (x ^ y ^ z) @@ -31,12 +35,9 @@ #define MD5STEP(f, w, x, y, z, data, s) \ w = rotlFixed(w + f(x, y, z) + data, s) + x - word32 a, b, c, d; + word32 b; - a=digest[0]; - b=digest[1]; - c=digest[2]; - d=digest[3]; + b=digest[0]; MD5STEP(F1, a, b, c, d, in[0] + 0xd76aa478, 7); MD5STEP(F1, d, a, b, c, in[1] + 0xe8c7b756, 12); @@ -106,10 +107,10 @@ MD5STEP(F4, c, d, a, b, in[2] + 0x2ad7d2bb, 15); MD5STEP(F4, b, c, d, a, in[9] + 0xeb86d391, 21); - digest[0]+=a; - digest[1]+=b; - digest[2]+=c; - digest[3]+=d; + a+=a; + digest[0]+=b; + c+=c; + d+=d; } NAMESPACE_END -- Jens Peter Secher _DD6A 05B0 174E BFB2 D4D9 B52E 0EE5 978A FE63 E8A1 jpsecher gmail com_ A. Because it breaks the logical sequence of discussion Q. Why is top posting bad? --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Crypto++ Users" group. To post to this group, send email to [EMAIL PROTECTED] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/cryptopp-users?hl=en -~----------~----~----~----~------~----~------~--~---
