giai thuat md5 message digest
TRANSCRIPT
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest
1.Giithiu
2.Thutng v k php3.M tthut ton
4.Tm lc
5.S khc nhau gia MD4 v MD5
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest1.Gii thiu
Gii thut c u vo l 1 thng ip(dng ch k) c di ty no ,qua qu trnh x l v phn tch s cho kt qu u ral mt dng nhn bit (tng t nh du im ch) di 128bit
hoc thng ip tm lc.Gii thut MD5 ng dng trn ch k s,ni m 1 file ln huht phi c m bo an ton d liu cng cc phng tinnh kha b mt v cng khai,v d nh h m RSA.
Gii thut MD5 c thit k chy kh hiu qu trn nhngh thng 32bit.Thm vo gii thut MD5 c th hin khngn gn
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Gii thut MD5-Message Digestc pht trin t gii thut ch k s MD4,MD5 c cc bc nhgn hn MD4 nhng kh thay i hn trong qu trnh thit k.
c nh gi l s dng nhanh chng hn MD4
m bo tc cng nh tnh bo mt
c cng nhn l gii thut t chun.
Da trn nn tng ca cng ngh OSI ,i tng ca MD5 cnh ngha
md5 OBJECT IDENTIFIER::
iso(1) member-body(2) US(840) rsadsi(113549)
digestAlgorithm(2) 5}
cc tham s ca MD5 cn phi c kiu NULL
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Gii thut MD5-Message Digest2.Thut ng v k php
Trong ti liu ny,1 t c di 32bit v 1 byte c di 8bit.S sp xp tun t ca cc bit c th l trnh t sp xp tnhin ca 1 byte ,ni m mi nhm lin tip nhau ca 8 bit lin
tc s biu din 1 byte v nhng byte u tin trong danh schcc byte l nhng byte quan trng (din t thuc tnh cat).Tng t nh vy,th t sp xp ca byte l th t ca 32 bitt.Nh vy mi nhm 4 byte lin tip s cho ta 1 t cng vi c
im t c trng nht ca n.
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Gii thut MD5-Message DigestK kiu ca k t + c ngha l cng t (i.e.,modulo-2^32 addition).K hiu X
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Gii thut MD5-Message Digest3.M t gii thut MD5
Chng ta bt u t gi s rng c 1 thng ip (ch k) c di bbit cho u vo.Gi s tm thy thng ip qua x l, y b l 1s nguyn kiu Interger.b c th nhn gi tr 0,khng nht thit l s
nguyn ln ca 8(bi ca 8) nn ta c th chn ty .Chng ta hnh dung ch k (thng ip ) c biu th nh sau:
m_0m_1m_{b-1}
Sau y l 5 bc k ha thng ip
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest3.1.Bc 1:Thm nhng bit m:Thng ip l m di ca n ng dng ti 448,theomodulo 512.Theo ,thng ip l m rng n trnh khng l 64
bit,m l biu th ca 512 bit di.Vic m lun c thc hin mc
d di ca thng ip ph hp ti 448 theo modulo 512.Vic m c thc hin nh sau:
Tng bit 1 c ni vo thng ip v sau 0 c ni vosao cho di bn trong thng ip m ph hp ti 448 theo modulo
512.Trong tt c,t nht 1 bit trong a s 512 bit ni vo b treo.
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest3.2.Bc 2:Ni di
Biu din 64 bit ca b ( di ca thng ip trc khi thmnhng mu m) c ni vo kt qu ca bc trc.Trong khi
b>2^64,ch 64 bit thp ca b c s dng.(Nhng mu ny c ni
vo nh hai t 32 bit v ni vo nhng t th t thp trc tinnh trong tha thun vi nhng qui nh trc).
Ti thi im ny,kt qu thng ip (sau khi ni cc mu vi b) c 1 di chnh xc 512 bit.Tng ng,thng ip ny c di chnh
xc ca 16 t 32 bit.
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest3.3.Bc 3:Khi to b m MD
Mt b m 4 t A,B,C,D c s dng tnh ton thng iptm lc. y tng t A,B,C,D ln lt l mt bn ng k 32
bit.Nhng bn ng k ny c khi to vi nhng gi tr trong
h 16,nhng byte thp trc tin.word A:01 23 45 67
word B:89 ab cd ef
word C:fe dc ba 98
word D:76 54 32 10
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Gii thut MD5-Message Digest
3.4.Bc 4:X l thng ip trong khi 16 tTrc ht chng ta nh ngha 4 hm ph m tng hm nhp vo 3 t32 bit v a ra u ra 1 t 32 bit
F(X,Y,Z) = XY v not(X)Z
G(X,Y,Z) = XZ v Ynot(Z)H(X,Y,Z) = X xor Y xor Z
I(X,Y,Z) = Y xor (X v not(Z))
Trong mi mu xc nh nhng hot ng ca F c iu kin:
If X then Y else Z
Hm F cho php s dng + thay cho v t XY v not(X)Z ,khngbao gi cng c trong 1 v tr bit.N ch n nhng iu nunhng bit ca X,Y v Z l c lp v ngang hng,mi bit ca
F(X,Y,Z) l c lp v ngang hng.
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Gii thut MD5-Message DigestCc hm G,H,I tng t nh hm F.Trong chng hnh ngsong song phn theo bit a ra u ra t nhng bit ca X,Y vZ.Trong mt trng thi nh vy nu cc bit ca X,Y,Z l c lpv ngang hng th mi bit ca G(X,Y,Z),H(X,Y,Z),I(X,Y,Z) cng
s c lp v ngang hng.Bc ny s dng 1 bng 64 yu t T[164] c xy dng thm sin.Yu t T[i] ca bng c biu th bng phn nguyn ca4294967296*abs(sin(i)),vi i l s radians bt k.
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Gii thut MD5-Message Digest//X l mi khi 16 t
for i =0 to n/16-1 do
for j = 0 to 15 do
Set X[j] to M[i*16+j].End//
/* Save A as AA, B as BB, C as CC, and D as DD. */
AA = A
BB = B
CC = C
DD = D
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Gii thut MD5-Message Digest/* Round 1. */
// [abcd k s i] hin th thao tc a = b + ((a + F(b,c,d) + X[k] + T[i])
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Gii thut MD5-Message Digest/* Round 2 [abcd k s i] hin th thao tc
a = b + ((a + G(b,c,d) + X[k] + T[i])
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Gii thut MD5-Message Digest/* Round 3. */
/* [abcd k s t] hin th thao tc
a = b + ((a + H(b,c,d) + X[k] + T[i])
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8/3/2019 Giai Thuat Md5 Message Digest
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Gii thut MD5-Message Digest/* Round 4. */
/* [abcd k s t] hin th thao tca = b + ((a + I(b,c,d) + X[k] + T[i])
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Gii thut MD5-Message Digest/*ri thc hin thm vo nh sau(tng dn mi bn ng k bigi tr ca n trc khi khi ny c khi ng)*/
A = A + AAB = B + BBC = C + CCD = D + DDEnd; /*lp trong i*/
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Gii thut MD5-Message Digest
3.5.Bc 5: u ra
Thng ip tm lc a ra u ra l A,B,C,D.Vi n,chngta bt u vi byte thp ca A v kt thc vi byte cao ca D
iu ny hon thnh s m t MD5.
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Gii thut MD5-Message Digest4.Tm lc
Gii thut thng ip tm lc thc hin n gin v cungcp 1 c im nhn dng hoc thng ip tm lc ca 1thng ip c di ty .N d on c nhng kh khn
khi tip xc vi 2 thng ip c cng ni dung tm lc lnhng hot ng trong bc ca 2^64,v kh khn ca vic in mt vi thng ip tm lc bt k cho trc hot ngtrong bc ca 2^128.
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Gii thut MD5-Message Digest5.S khc nhau gia MD4 v MD5
+ Mt vng trn th t c thm vo
+Mi bc by gi c 1 hng s cng duy nht
+ Hm G trong vng 2 c thay i t (XY v XZ v YZ)sang (XZ v Ynot(Z)) lm G t i xng hn
+Mi bc by gi thm kt qu ca bc k trc
+Cc t nhp vo theo th t no c truy nhp trong cc
vng 2 v 3 c thay i lm cho nhng mu ny t nh hngln nhau.