A new remote user authentication scheme for multi-server architecture

Transcription

1 Future Generaton Computer Systems 19 (2003) A new remote user authentcaton scheme for mult-server archtecture Iuon-Chang Ln a, Mn-Shang Hwang b,, L-Hua L b a Department of Computer Scence and Informaton Engneerng, Natonal Chung Cheng Unversty, Chay, Tawan, ROC b Department of Informaton Management, Chaoyang Unversty of Technology, 168, Gfeng E. Road, Wufeng, Tachung County 413, Tawan, ROC Receved 2 November 2001; receved n revsed form 1 March 2002; accepted 19 Aprl 2002 Abstract Remote user authentcaton s used to valdate the legtmacy of a remote logn user. Conventonal user authentcaton schemes are suted to solve the prvacy and securty problems for the sngle clent/server archtecture envronment. However, the use of computer networks and nformaton technology has grown spectacularly. More and more network archtectures are used n mult-server envronments. In ths paper, we propose a new remote user authentcaton scheme. The scheme can be used n mult-server envronments. In our scheme, the system does not need to mantan any verfcaton table, and the users who have regstered n the servers do not need to remember dfferent logn passwords for varous servers. In addton, our scheme can also wthstand replay and modfcaton attacks. Furthermore, t allows users to choose ther passwords freely, and a user can be removed from the system easly when the subscrpton expres Elsever Scence B.V. All rghts reserved. Keywords: Cryptography; User authentcaton; Remote logn; Securty 1. Introducton In a mult-server network archtecture, a network user must prove to the servers that he/she s a legtmate remote logn user before he/she can get any servce from the varous servers. In conventonal password authentcaton methods, each network user does not only need to log nto varous remote servers repettvely but also needs to remember varous user IDs and passwords. Therefore, users often have to wrte down ther numerous IDs and passwords. Ths s Ths research was partally supported by the Natonal Scence Councl, Tawan, ROC, under contract no.: NSC E Correspondng author. Fax: E-mal addresses: cln@cs.ccu.edu.tw (I.-C. Ln), mshwang@cyut.edu.tw (M.-S. Hwang). nsecure because these IDs and passwords may easly leak out. Another problem n usng tradtonal remote logn methods to authentcate a user s that the server often uses a verfcaton table that stores each user s ID and password. Therefore, the server requres extra memory space to store the verfcaton table. Furthermore, the server must mantan and protect the table from beng modfed by an ntruder. If the verfcaton table can be read or altered by an ntruder, then the ntruder can also append a new ID and password to the table. Stll another problem arses when the communcaton lnk between the termnal and the system s nsecure. An ntruder can dscover a remote user s password and replay the message to break n the system later. Even f the password s encrypted durng transmsson [19,22], the ntruder can stll replay the prevously ntercepted logn message to X/02/$ see front matter 2002 Elsever Scence B.V. All rghts reserved. PII: S X(02)

2 14 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) mpersonate the legtmate user. An effcent, secure remote user authentcaton system must agree wth the mult-server archtecture and wthstand these attacks [18]. Accordng to the dscussons here, an effcent remote password authentcaton scheme must not only perform the transacton correctly, but also meet the followng requrements: It agrees wth a mult-server network archtecture wthout repettve regstraton. It needs no password tables or verfcaton tables. It can wthstand the replay attack and guessng attack [13]. It allows a user to choose hs/her ID and password freely. In ths paper, we shall propose an effcent remote user authentcaton scheme based on the smple geometrc propertes of the Eucldean plane. Ths scheme can satsfy all the requrements for authentcaton just above. Before descrbng the proposed scheme, we wll frst brefly revew related works on remote password authentcaton schemes. Please note that the schemes to be revewed have already solved the problems of remote user authentcaton n sngleserver network archtectures. These revewed schemes do not yet agree wth mult-server network archtectures. After the revew, we shall propose our new remote password authentcaton scheme for mult-server archtectures. Next, the securty of our proposed scheme wll be analyzed. Fnally, we shall state our conclusons n the last secton of the paper. 2. Lterature revew In ths secton, some related works n the area of remote password authentcaton schemes wll be ntroduced. A typcal remote password authentcaton system conssts of two knds of partcpants, a remote user and a server. The server verfes the password of the logn user and provdes servce for a legtmate logn user. Typcally, a remote user authentcaton protocol conssts of three phases: (1) regstraton phase, (2) logn phase and (3) server authentcaton phase. A new user must frst regster wth the server. After regstraton and authorzaton, the user can logn to the server for servce. The orgnal concept of password authentcaton schemes s based on one-way hash functons [8,12, 15,20,21,26]. In these schemes, the problems of mpersonaton and modfcaton arse. An ntruder can modfy the passwords stored n the verfcaton table. These schemes cannot wthstand a replay attack. In 1981, a new remote password authentcaton scheme was proposed by Lamport [17]. Hs scheme can wthstand the replay attack, but not the modfcaton attack. Lamport s scheme requres a password table, stored n the computer system, whch could be modfed by an ntruder. To solve the problems, Horng [9] and Jan and Chen [16] proposed a password authentcaton scheme wthout verfcaton tables or password tables. Another nteractve password authentcaton scheme, based on publc-key cryptography, such as the Dffe Hellman cryptosystem [6] and RSA cryptosystem [23], was proposed by Sngh [25]. Ths scheme can wthstand the replay attack, but t requres multple communcatons between the user and the computer system. In [14], Hwang et al. proposed an authentcaton scheme usng a smart card. Ther scheme was based on Shamr s ID-based sgnature scheme [24]. One year later, Chang and Wu [5] proposed a smlar scheme also wth a smart card based on the Chnese remander theorem (CRT). Unfortunately, that scheme was vulnerable and was n fact broken by Chang and Lah [3]. In ther scheme, each user holds a smart card n whch the nformaton could be read easly. Therefore, the secret encrypton keys can easly be uncovered. In [1], Chang et al. proposed an authentcaton scheme that ntroduced tmestamps nto the authentcaton algorthm. Although ths scheme can guard aganst an attack that uses the replay of an ntercepted logn message, t has one major weakness. The user s not permtted to choose hs/her dentty and password freely. Smlar problems also occurred n Chang and Hwang s scheme [2]. In 1995, Wu proposed an effcent remote logn authentcaton scheme [28], whch s based on the smple geometrc property of the Eucldean plane. The prmary advantage of ths scheme s that users are permtted to choose and change ther passwords freely. However, ths scheme s vulnerable and broken n [11]. In addton, n ths scheme, the authorzaton cannot be easly receved from a legal user, and the scheme does not agree wth a mult-server envronment. Later,

3 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) the proposed schemes n [4,27,29] also suffer from the smlar problems. Recently, Hwang [10] proposed a new remote password authentcaton scheme based on the ElGamal dgtal sgnature method [7]. Ths new remote password scheme stll does not agree wth the mult-server envronment. Recently, L et al. [18] proposed a remote password authentcaton scheme by usng neural networks. It agrees wth the mult-server envronment. However, t spends too much tme on tranng neural networks. In the next secton, we shall propose a new, effcent user authentcaton scheme that allows password authentcaton n a mult-server archtecture. 3. A new authentcaton scheme for mult-server archtecture In ths secton, we shall propose an effcent remote user authentcaton scheme for mult-server archtectures. There are three knds of partcpants n our scheme: the logn users, the varous servers, and a central manager (CM). In ths scheme, we assume the CM can be trusted. The CM sets up several publc and secret parameters. Each legtmate user can get servce granted from the servers where he/she has regstered. The user does not need to do repettve regstratons wth varous servers. The proposed password authentcaton scheme can be dvded nto four phases: (1) the ntalzaton phase, (2) the regstraton phase, (3) the logn phase and (4) the authentcaton phase. In the ntalzaton phase, the CM sets up and publshes some nformaton. To obtan each server s secret and publc keys, n the regstraton phase, a new user chooses hs/her own dentfcaton name and password. In the logn phase, when a legtmate user wants to log nto the server, he/she must pass the dentfcaton. Then the server wll verfy the legtmacy of the logn user n the authentcaton phase. The detals of the proposed remote password authentcaton scheme for mult-server archtectures are descrbed as follows The ntalzaton phase Assume that S m s a set of servers n a mult-server envronment, where S m : {Ser 1, Ser 2,...,Ser m }. Intally, CM chooses two system parameters p and g, where p s a large prme and g s a generator of order p n Zp. To publsh p and g, both p and g can be shared among the system of servers. CM then chooses a secret key d for each server Ser, where s from 1 to m. These parameters all belong to the Galos feld GF(p). Up to ths pont, each server Ser has a publc key e and a secret key d. The securty comes from the dffculty of solvng the dscrete logarthm problem n a fnte feld, whch s smlar to the ElGamal scheme [7]. The steps are as follows: (1) CM selects a large prme p and a prmtve number g of GF(p). (2) CM chooses each server s secret key d and calculates the publc key e as follows: e = g d mod (p 1). (1) Each server Ser has the key par (e, d ) The regstraton phase When a new user wants to log nto the mult-server computer system, the user must regster wth the server frst. Assume that the new user s granted regstraton only by a set S n of servers, where S n S m, the regstraton steps are as follows: (1) Frstly, the new user chooses hs/her own dentty ID and password PW, then delvers ID and PW to CM. (2) Suppose that S n s a set of servers. Wth whch the new user can regster. CM calculates X = ID e mod p, (2) Y = ID d mod p, (3) D = e ID mod p (4) and W = e PW mod p, (5) and (X,Y ) s a pont n the space of real numbers for server Ser whle (D,W ) s another pont n the space of real numbers for the new user, where Ser S n. (3) Accordng to the two ponts (X,Y ) and (D,W ), CM can construct a lne L. Here, L : Y = f(x) = ax + b mod p, where a = (W Y )/(D X ) mod p and b = Y X ((W Y )/(D X )) mod p.

4 16 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) (4) CM randomly chooses a lne LS, where LS = g(x) = a X + b mod p. Accordng to the two lnes L and LS, CM can obtan an ntersecton pont (K,Q ) for each server Ser S n. (5) Assume that the server Ser provdes servce for the new user and that SP s the servce perod for each server Ser. SP ncludes the user s dentty and the servce expraton date. If the server does not provde servce for the new user, the servce perod s 0. To sgn each servce perod SP,we use ElGamal [7] dgtal sgnatures. To fulfll ths, CM frst chooses a random number k for server Ser such that k s relatvely prme to p 1. Then CM keeps k secret. Next, we calculate r = g k mod p. (6) By usng the extended Eucldean algorthm, we obtan s n the followng equaton: SP = (d r + k s ) mod (p 1). (7) The sgnature of servce perod SP wth server Ser s the par (r,s ). (6) Once the regstraton phase s completed by CM, whose man role s to delver the publc parameters {SP, (r,s ), K } and LS to the regstered user, these parameters can be stored n the smart card or other storage devces. The concept of the regstraton phase s shown n Fg The logn phase In ths phase, users are authorzed to use multple servers once they have made ther way through the password authentcaton. Assume that S n s a set of servers that a regstered user wants to log n. The user frst keys n hs/her ID and password, and then the authentcaton system wll perform the followng steps: (1) The system obtans a tme sequence T whch s lke a tmestamp from the termnal. (2) Afterwards, the system wll generate a secret random number Ran and compute the two values A and B as follows: A = g Ran mod p, B = e Ran T mod p. (3) The value Q can be calculated from the lne LS and K, where LS : g(k ) = Q. Then the system wll calculate (D,W ) from Eqs. (4) and (5). Accordng to the two ponts (K,Q ) and (D,W ), the system can reconstruct the lne L : f(x) = Y. (4) Then the system wll calculate Z from L usng B,.e., Z = f(b ). Then, the system wll send Fg. 1. The concept of the regstraton phase.

5 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) message M to Ser, where message M ncludes [ID,(K,Q ), Z,A,T,SP,(r,s )]. The user can also log nto another regstered server at the same tme The authentcaton phase In the authentcaton phase, the server receves the message M at T and performs the followng tasks to authentcate the user s logn request. (1) The server shall check whether the tme nterval between T and T s greater than T, where T denotes the expected legal tme nterval for transmsson delay between the logn termnal and the server Ser.If(T T) T, the message M mght have been replayed, and the server wll reject the logn request. (2) Next, the server checks the correctness of ID. If the format of ID s ncorrect, the server wll reject the logn request. (3) Ser checks the valdty of the servce perod SP. If the servce perod s overdue, the server wll reject the logn request. Otherwse, the server checks whether the followng equaton holds e r r s = g SP mod p. (8) If the above equaton does not hold, the server rejects the logn request. (4) Ser computes the value B B = A d T mod p = (g Ran ) dt mod p = e Ran T mod p. (9) Accordng to the two ponts (K,Q ) and (B,Z ), Ser can reconstruct the orgnal lne L. (5) Fnally, the server Ser calculates the pont (X,Y ) followng Eqs. (2) and (3). If the pont s on the lne L (f(x ) = Y ), the server wll accept the logn request; otherwse, t wll reject the logn request To change password In ths proposed scheme, users can choose and change ther passwords freely. When a user wants to change hs or her password at server Ser, the steps are as follows: (1) The user should type the old password and the new password. (2) The system reconstructs the lne L : f(x) = y for the server Ser. The step s smlar to step 3 as descrbed n the logn phase. Fg. 2. The concept of the process of changng passwords.

6 18 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) (3) Then we can calculate the value Y from f(x ), where X can be calculated through Eq. (2). Accordng to the new password, we obtan the new pont (D,W ) va Eq. (5). (4) The new lne L s reconstructed by the two ponts (D,W ) and (X,Y ). The new ntersecton pont (K,Q ) can be obtaned from the lnes L and LS. (5) Fnally, we update the value K nto K. In ths process, we need no connecton to the servers,.e., we can change passwords off lne. The concept of the process s shown n Fg Example In ths secton, we gve an example to llustrate how the proposed scheme works. We assume that there are three servers n ths example The ntalzaton phase In ths phase, CM selects p, g and calculates the key par (d 1,e 1 ), (d 2,e 2 ) and (d 3,e 3 ) for severs Ser 1, Ser 2 and Ser 3 usng e = g d mod p, = 1, 2, The regstraton phase Assume that a new user U 1 s granted to regster only from the servers Ser 1 and Ser 3. The concept of regstraton s shown n Fg. 3 and the process steps are as follows: (1) The new user chooses hs own dentty ID and password PW, then sends the par of (ID, PW) to CM. (2) CM calculates the set of two ponts [(X 1,Y 1 ), (D 1,W 1 )] for Ser 1 and [(X 3,Y 3 ), (D 3,W 3 )] for Ser 3 usng Eqs. (2) (5). (3) Accordng to the set of two ponts, CM constructs two lnes; L 1 for Ser 1 and L 3 for Ser 3. (4) CM randomly chooses a lne LS, LS : g(x) = y. Accordng to the lnes L 1,L 3 and LS, CM can obtan ntersecton ponts (K 1,Q 1 ) and (K 3,Q 3 ). (5) The servers, Ser 1 and Ser 3, provde servces for the new user and recall the servce perod for Ser 1 and Ser 3 wth SP 1 and SP 3, respectvely. CM uses ElGamal dgtal sgnatures scheme to sgn each servce perod. The sgnatures for SP 1 and SP 3 are (r 1,s 1 ) and (r 3,s 3 ), respectvely. (6) CM delvers the parameters [SP 1,(r 1,s 1 ), K 1 ], [SP 3,(r 3,s 3 ), K 3 ], and the lne LS to the new user. Fg. 3. An example n step 2 of the regstraton phase.

7 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) Fg. 4. The concepts of logn and authentcaton phase The logn phase In ths phase, we assume that a user wants to log nto the server Ser 3. The logn phase perform the followng steps. (1) The user keys n hs ID and password and system obtans the tme sequence T. (2) Then t generates a secret random number Ran 3 and calculates the values A 3 and B 3 usng A 3 = g Ran 3 mod p and B 3 = e Ran 3 T 3 mod p. Furthermore, system calculates Q 3 by usng LS : Q 3 = g(k 3 ). (3) The system reconstructs the lne L 3 from the two ponts (K 3,Q 3 ) and (D 3,W 3 ). The archtecture s shown n Fg. 4(a). Here, the pont (D 3,W 3 ) s calculated usng Eqs. (4) and (5). (4) Fnally, system computes L 3 : Z 3 = f(b 3 ) and sends message [ID,(K 3,Q 3 ), Z 3,A 3,T, SP 3,(r 3,s 3 )]toser The authentcaton phase Assume that the server Ser 3 receves the message M at the tme sequence T. The server Ser 3 performs the followng authentcaton phases. (1) Ser 3 checks whether the tme nterval T between logn tme (T) and the server system tme (T ). (2) Ser 3 checks the correctness of ID. (3) Verfy the sgnature (r 3,s 3 ) wth the servce perod SP 3 usng Eq. (8). If the sgnature s correct, Ser 3 wll check whether the servce perod SP 3 s overdue. (4) Ser 3 calculates B 3 as follows: A d 3T 3 mod p = (g Ran 3 ) d3t mod p = e Ran 3T 3 mod p = B 3. Accordng to the two ponts (K 3,Q 3 ) and (B 3,Z 3 ), Ser 3 reconstructs the orgnal lne L 3 as shown n Fg. 4(b). (5) Ser 3 then computes the pont (X 3,Y 3 ) usng Eqs. (2) and (3). If the pont s located on the lne L 3, then Ser 3 wll accept the logn request of the user. 5. Securty analyss In ths secton the securty of the proposed remote password authentcaton scheme s examned Secrecy In our scheme, both the secret key d of server Ser and the password PW of the user must be kept secret. Furthermore, the user stores some mportant nforma-

8 20 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) ton, such as the users dentty (ID), the servce perod (SP ), the sgnature (r,s ), (K ) and the lne LS. If d or PW leaks out, then the system wll become nsecure because an ntruder can reconstruct the lne L and fnd the pont (X,Y ) of the server easly, and then he/she can mpersonate the legal user. Thus, the two parameters d and PW must be kept secret. Our scheme s based on the ElGamal dgtal sgnature scheme. The securty comes from the dffculty of calculatng dscrete logarthms. Therefore, to derve the secret key d from Eq. (1) s dffcult. In addton, only legal users can compute W and reconstruct the lne L wth Ser from the two ponts (K,Q ) and (D,W ). Then, they can derve the correct Z from the equaton f(b ) = Z. Thus, wthout the vald password, any llegal user, not knowng the pont (D,W ), cannot reconstruct the lne L and the secret pont (X,Y ) of Ser. We have presented an example for examnaton n Secton 4. Although the ntruder can ntercept the logn request message M, however, wthout the secret parameter d, he/she cannot obtan B drectly from Eq. (9). Therefore, the ntruder only knows the ponts (K 3,Q 3 ) and the parameters X 3, D 3 and Z 3. Obvously, the ntruder does not have enough ponts to reconstruct the lne L. It s dffcult for the ntruder to reconstruct the lne L 3 as shown n Fg Non-forgery Assume that an ntruder wants to pretend to be a legal user to logn wth the server Ser. For remote access, the ntruder can prevously ntercept a logn request ncludng [ID,(K,Q ), SP,(r,s )]. The ntruder can also forge A,B and T easly. However, the key pont s that the ntruder cannot obtan the lne L ; thus, Z cannot be solved n step 4 of the logn phase. Supposng the ntruder attempts to forge the value Z and sends the logn message [ID j,(k,q ), A,Z,T, SP,(r,s )] to the server. Although the server can recover B from Eq. (9), the server wll reject the logn request n step 5 of the authentcaton phase. Therefore, the ntruder cannot mpersonate a legal user, whch, agan, shows our scheme can wthstand the mpersonaton attack Replay resstance To resst the replay attack, our scheme uses the concept of tmestamp. When the ntruder replays the prevously ntercepted logn messages and wants to masquerade as a legal user. In order to pass the test n step 1 of the authentcaton phase, the ntruder must change T nto a new tme T such that (T T ) T, where T s the tmestamp gven Fg. 5. It s dffcult to reconstruct the lne L 3.

9 I.-C. Ln et al. / Future Generaton Computer Systems 19 (2003) at the tme when the server receves the llegal logn message. Once T s changed, the value of B s changed too. However, the ntruder cannot acqure the vald Z because the lne L s secret. Ths s the property of non-forgery. The ntruder wll fal the test n the authentcaton phase. Therefore, the proposed scheme s secure aganst the replay attack. The proposed scheme detects replays of the logn message by testng (T T) T. However, ths test may come to the two undesred results as follows. One result s that T s small and the server denes legtmate authentcaton requests. Ths wll result n a possble network delay or the loss of clock synchronzaton. The other s that T s large and the server cannot resst the replay attack. Thus, t s mportant here to choose an approprate T. One of the solutons s to use a replay detecton buffer whch keeps the clock synchronzaton. The server can change T accordng to the traffc loadng and clock synchronzaton The resstance of extendng the servce perod In our proposed scheme, the servce perod s used to manage the legal users. When the servce perod s exceeded, the user must re-regster for extendng the servce perod. Otherwse, the user wll become an llegal user. To prevent the user from llegally extendng the servce perod, we use the ElGamal dgtal sgnature scheme [7]. The securty of ths scheme comes from the dffculty of calculatng dscrete logarthms. Each server sgns for the servce perod usng Eqs. (6) and (7). In the authentcaton phase, the server frst tests the sgnature usng Eq. (8). In case that a user wants to extend hs/her servce perod, that means the user has to modfy hs/her SP to SP. However, the user cannot obtan the secret key from the server; therefore, he/she cannot calculate the correct s for Eq. (7),SP = (d r +k s )( mod P 1), and for Eq. (8). Obvously, the test wll be faled. Therefore, the servce perod cannot be modfed by any user n our proposed scheme. 6. Conclusons and dscusson In ths paper, we have proposed an effcent remote user authentcaton scheme. The server stores only ts key par (e,d ), and each regstered user stores the nformaton [SP,(r,s ), K ], and a lnear formula LS. Ths scheme s constructed based on the ElGamal dgtal sgnature scheme and the smple geometrc propertes on the Eucldean plane. Ths scheme authentcates the valdty of a logn user wthout usng any verfcaton table or password fle. The scheme uses the tmestamp technque to work aganst the replay attack. It s proven that our new scheme can wthstand both the modfcaton attack and the replay attack. The major breakthrough of ths scheme s that t agrees not only wth mult-user networks but also wth mult-server networks. The user can log nto varous servers at the same tme wthout repettve regstratons wth all the servers. Furthermore, the system can manage user s prvleges by usng the servce perod. When the servce perod of a user expres, the central authorty wll stop the servce for that user. Another advantage of ths scheme s that users can freely choose and change ther passwords off lne. Acknowledgements The authors wsh to thank many anonymous referees for ther suggestons to mprove ths paper. Part of ths research was supported by the Natonal Scence Councl, Tawan, ROC, under contract no. NSC E References [1] C.C. Chang, R.J. Hwang, J.B. Danel, Usng smart cards to authentcate passwords, n: Proceedngs of the IEEE Internatonal Carnahan Conference on Securty Technology, 1993, pp [2] C.C. Chang, S.J. Hwang, Usng smart cards to authentcate remote passwords, Comput. Math. Appl. 26 (7) (1993) [3] C.C. Chang, C.S. Lah, Remote password authentcaton wth smart cards (correspondence), IEE Proc. E 139 (4) (1992) 372. [4] C.C. Chang, S.M. Tsu, C.Y. Chen, Remote scheme for password authentcaton based on theory of quadratc resdues, Comput. Commun. 18 (1995) [5] C.C. Chang, T.C. Wu, Remote password authentcaton wth smart cards, IEE Proc. E 138 (3) (1991) [6] W. Dffe, M.E. Hellman, New drectons n cryptography, IEEE Trans. Inform. Theory 22 (1976) [7] T. ElGamal, A publc-key cryptosystem and a sgnature scheme based on dscrete logarthms, IEEE Trans. Inform. Theory 31 (4) (1985)

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