Anonymous A ibu e-based C eden ials in Collabo a i e Indoo
Posi ioning Sys ems
Ra´
ul Casano a-Ma qu´
es1,2 a, Pa el Pascacio2,3 b, Jan Hajny1 c and Joaqu´
ın To es-Sosped a2,4 d
1Depa men o Telecommunica ions, B no Uni e si y o Technology, B no, Czech Republic
2Ins i u e o New Imaging Technologies, Uni e si a Jaume I, Cas ell´
on, Spain
3Elec ical Enginee ing Uni , Tampe e Uni e si y, Tampe e, Finland
4UBIK Geospa ial Solu ions S.L., Cas ell´
on, Spain
Keywo ds: A ibu e-based C eden ials, Collabo a i e Indoo Posi ioning Sys ems, P i acy, Anonymi y, Blue oo h Low
Ene gy, Wea ables.
Abs ac : Collabo a i e Indoo Posi ioning Sys ems (CIPSs) ha e ecen ly ecei ed conside able a en ion, mainly be-
cause hey add ess some exis ing limi a ions o adi ional Indoo Posi ioning Sys ems (IPSs). In CIPSs, Blue-
oo h Low Ene gy (BLE) can be used o exchange posi ioning da a and p o ide in o ma ion ( he Recei ed
Signal S eng h Indica o (RSSI)) o es ablish he ela i e dis ance be ween he ac o s. The collabo a i e mod-
els exploi he posi ion o ac o s and he ela i e posi ion among hem o allow posi ioning o ex e nal ac o s
o imp o e he accu acy o he exis ing ac o s. Howe e , he adi ional p o ocols (e.g., iBeacon) a e no ye
eady o p o iding su icien p i acy p o ec ion. This pape deals wi h p i acy-enhancing echnologies and
hei applica ion in CIPS. In pa icula , we ocus on c yp og aphic schemes which allow he e i ica ion o
use s wi hou hei iden i ica ion, so-called Anonymous A ibu e-based C eden ial (ABC) schemes. As he
main con ibu ion, we p esen a c yp og aphic scheme ha allows secu i y and p i acy- iendly sha ing o
loca ion in o ma ion sen h ough BLE ad e ising packe s. In o de o demons a e he p ac icali y o ou
scheme, we also p esen he esul s om ou implemen a ion and benchma ks on di e en de ices.
1 INTRODUCTION
Wi-Fi and BLE inge p in ing a e popula echniques
o p o iding indoo posi ioning. They ely on he
signal s eng h om mul iple emi e s (ei he Wi-Fi
Access Poin s (APs) o BLE beacons). Howe e , he
Recei ed Signal S eng h (RSS) da a used o es ima e
he posi ions ha e a s ong noise componen , he e-
o e ha ing a gene al posi ioning accu acy a me e
le el (i.e., a ew me e s) (Mau z, 2012). In addi ion,
he deploymen complexi y, as well as elying on an
in as uc u e o beacons and se e s, ha e become
a se ious p oblem o la ge o ganiza ions all a ound
he wo ld. Wea able-based CIPSs a e inc easingly be-
coming popula o e he las ew yea s as a solu ion
o add ess hose p oblems in indoo posi ioning (Pas-
cacio e al., 2021). The CIPSs use he loca ion o a
ah ps://o cid.o g/0000-0001-6653-867X
bh ps://o cid.o g/0000-0001-9206-7496
ch ps://o cid.o g/0000-0003-2831-1073
dh ps://o cid.o g/0000-0003-4338-4334
se o ac o s and hei ela i e dis ances o 1) p o ide
localiza ion o ex e nal use s and/o 2) imp o e he
posi ioning accu acy o he cu en use s ha a e col-
labo a ing (Khandke e al., 2019).
Wea able de ices a e equipped wi h buil -in ech-
nologies such as Wi-Fi and Blue oo h, which a e ca-
pable o es ima ing use s’ posi ions and ubiqui y in
indoo en i onmen s. In pa icula , CIPSs app oaches
based on BLE a e one o he mos popula solu ions.
Sma phones can send BLE ad e isemen packe s
(e.g., iBeacon), which can be used la e o compu e
he ela i e dis ances be ween hem wi h he ga he ed
RSS alues. This al e na i e p esen s a s aigh o -
wa d deploymen and a good ade-o be ween powe
consump ion and pe o mance (Yang e al., 2020).
Howe e , high in e -connec i i y o unknown de ices
and he lack o s ong communica ion p o ocols in
e ms o secu i y and p i acy ep esen a weakness.
Malicious ac o s could pe o m a acks such as spoo -
ing o ea esd opping in unsecu ed collabo a i e sys-
ems (Chebli e al., 2019). These issues encou aged
he de elopmen o mo e p i acy- iendly solu ions.
Casano a-Ma qués, R., Pascacio, P., Hajny, J. and To es-Sosped a, J.
Anonymous A ibu e-based C eden ials in Collabo a i e Indoo Posi ioning Sys ems.
DOI: 10.5220/0010582507910797
In P oceedings o he 18 h In e na ional Con e ence on Secu i y and C yp og aphy (SECRYPT 2021), pages 791-797
ISBN: 978-989-758-524-1
Copy igh c
2021 by SCITEPRESS – Science and Technology Publica ions, Lda. All igh s ese ed
791
Exis ing CIPS a e based on cen alized schemes.
A se e -based solu ion acili a es mo e complex a -
acks such as use aceabili y o linkabili y o com-
munica ions. Thus, i is necessa y o mo e o a decen-
alized app oach. Building a decen alized CIPS us-
ing BLE echnology ep esen s a majo challenge due
o he educed space a ailable in BLE packe s, which
depends on he Blue oo h e sion (Blue oo h SIG,
2019). This hinde s he use o s anda d algo i hms
such as RSA, DH o AES o in o ma ion enc yp-
ion and use au hen ica ion. A ibu e-based au hen-
ica ion schemes allow use s o anonymously and se-
lec i ely p o e possession o hei pe sonal a ibu es
such as age, ci izenship, nega i e SARS-CoV-2 es
o loca ion da a. Ellip ic cu e c yp og aphy and he
educed size o i s keys can ackle he a o emen ioned
p oblems and p o ide anonymi y, unlinkabili y, un-
aceabili y and selec i e disclosu e o a ibu es.
In ligh o he iden i ied p oblems, in his wo k
we pu sue he decen aliza ion o collabo a i e indoo
posi ioning sys ems based on BLE beacons, while
p o iding, h ough ellip ic cu e c yp og aphy and
anonymous a ibu e-based au hen ica ion schemes, a
secu e and p i acy- iendly sys em o exchanging lo-
ca ion da a.
1.1 Rela ed Wo k
In he li e a u e he e a e se e al a icles ha add ess
anonymi y, secu i y, and p i acy issues o IPSs om
di e en pe spec i es (e.g., Wi eless Senso Ne wo k
(WSN) o In e ne o Things (IoT)). Howe e , only
e y ew o hem ocus on collabo a i e posi ioning
and/o BLE beacon app oaches. One o he mos in-
e es ing pape s is p oposed by (Kang e al., 2018),
which is based on he open-sou ce Eddys one BLE
o ma p oposed by (Hassidim e al., 2016). Eddy-
s one BLE o ma in oduces a scheme o mi iga e
acking and secu i y h ea s. The co e o he scheme
is cloud-based Epheme al Iden i ie s (EID), which en-
su es only au ho ized membe s o p ope ly iden i y
he BLE s anda d beacons.
Up o now, a oo li le a en ion has been paid
o CIPSs. (Zidek e al., 2018) de eloped a scheme
named Bell ock which combines an ecosys em o
s anda d beacons and use -based beacons. Bell-
ock p o ides access con ol o s anda d beacons
and anonymi y o use -based beacons by using h ee
echniques o gene a e pseudo-anonymous iden i ie s
( andom, synch onized, and enc yp ed) ha can be
unmasked by a se e .
(Des ia i e al., 2017) p oposed he Da a T ans-
mission Scheme o Indoo Mobile Coope a i e Lo-
caliza ion Sys em ha wo ks o e Wi-Fi. The scheme
uses AES-128 o enc yp he message, MD5 o con-
s uc he HMAC and RSA-2048 o enc yp bo h he
AES key and he HMAC. Thei app oach migh no
be well sui ed as he sys em emains ulne able o
man-in- he-middle a acks du ing he RSA key-pai
exchange, leading o a o al loss o con iden iali y and
message in eg i y.
A key p oblem wi h he a o emen ioned p opos-
als lies in se e -dependency, u ning he sys em in o
a cen alized en i onmen . This me hod could su e
om a ple ho a o pi alls such as denial o se ice
(DoS), spoo ing, e c.
Some p elimina y wo k on ABCs was ca ied
ou se e al decades ago by (Chaum, 1985), (B ands,
2000), and (Camenisch and Lysyanskaya, 2001). In
subsequen yea s, much mo e in o ma ion on ABCs
has become a ailable abou p ac ical applica ions
(A aoui e al., 2015), e oca ion p o ocols (Ca-
menisch e al., 2010) and he use o mo e e icien
algeb aic s uc u es (Chase e al., 2014), (Ba ki e al.,
2016), and (Ringe s e al., 2017). Due o he high
compu a ional complexi y equi ed by hese schemes,
p ac ical implemen a ion on cons ained de ices is
s ill a challenge, esea che s need o ind a scheme
ha sa is ies hei speci ic needs. As a as we know,
no s udies ha e been published on ABC schemes ap-
plied o CIPSs.
1.2 Ou Con ibu ion
In o de o ill he gap ound in he li e a u e, we p o-
pose a new decen alized p i acy-p ese ing use au-
hen ica ion mechanism o CIPSs wi h ABC. Ou
solu ion combines ze o-knowledge p oo s wi h a e-
oca ion scheme based on li e ime and p o ides
anonymi y, unlinkabili y and un aceabili y.
The main con ibu ions a e he ollowing:
• To he bes o ou knowledge, we p esen he i s
decen alized secu i y scheme o CIPSs based on
BLE ad e ising.
• We de ine a scheme ha p o ide anonymous lo-
ca ion da a sha ing, decen alized au hen ica ion
and o line e oca ion.
• We p o ide a secu i y analysis on he p oposed
solu ion.
• We desc ibe he implemen a ion esul s.
The es o he pape is o ganized as ollows. Sec-
ion 2 gi es a b ie o e iew o he sys em model.
Sec ion 3 ho oughly de ails he c yp og aphic design
o he scheme. Sec ion 4 analyzes he secu i y. Sec-
ion 5 p esen s he implemen a ion esul s. Finally,
Sec ion 6 epo s some conclusions.
SECRYPT 2021 - 18 h In e na ional Con e ence on Secu i y and C yp og aphy
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2 SYSTEM OVERVIEW
The sys em model is depic ed in Figu e 1 and consis s
o he ollowing en i ies:
•Issue (I): is esponsible o issuing he pe sonal
a ibu e mID o a use using he Issue algo i hm.
The mID a ibu e ep esen s he use iden i ie
ob ained du ing egis a ion in he sys em. The
Issue algo i hm p o ides he use wi h c yp o-
g aphically signed c eden ials ha a e alid wi hin
he sys em. Access c eden ials consis o he al-
ues σ,σx0,σx ,σxID .
•Re oca ion Au ho i y (RA): emo es in alid
use s. Access con ol is achie ed h ough he e-
oca ion c eden ial σx , issued om he e oca-
ion a ibu e m . A emp ing o au hen ica e wi h
he e oked c eden ials will esul in ailu e. To
educe he complexi y o he sys em, we will con-
side om now on he e oca ion au ho i y and he
issue as he same en i y (I).
•Use (U): en olls in he sys em o use he col-
labo a i e indoo posi ioning sys em. E e y use
holds unique c eden ials gene a ed by he issue
and he e oca ion en i y (σ,σx0,σx ,σxID ), hen,
he use can anonymously p o e hei possession
o he e i ie using he Show algo i hm.
•Ve i ie (V): e i ies he possession o he use a -
ibu e using he Ve i y algo i hm. I he a ibu e
owne ship is e i ied success ully, he e i ie will
be able o use he loca ion in o ma ion o posi ion
hemsel . O he wise, he in o ma ion is ejec ed.
Issue Re oca ion Au ho i y
Show
Ve i y
IssueIssue
Use Ve i ie
Figu e 1: Sys em s uc u e.
Ini ially, all de ices egis e ed in he sys em beha e as
Use s. When one o hem needs o imp o e i s posi-
ion, i empo a ily assumes he ole o Ve i ie . This
ole can be used o ensu e ha he in o ma ion is p o-
ided by a alid use .
The e a e wo modes o ope a ion o he Use and
Ve i ie oles: he ac i e mode and he passi e mode.
Use ope a ion modes: 1) Ac i e mode: esponds
o e i ie eques s and assis s hem wi h posi ioning
by ac i ely pa icipa ing in he sys em. 2) Passi e
mode: emains unno iced in he sys em and does no
espond o e i ie eques s. In his mode, he use
does no in e ac wi h he sys em.
Ve i ie ope a ion modes: 1) Ac i e mode: ac i ely
eques s loca ion da a om nea by use s o imp o e
i s posi ion. 2) Passi e mode: emains hidden in he
sys em and wai s o o he e i ie s o eques loca ion
da a. In his mode, posi ioning is no possible i he e
a e no ac i e e i ie s nea by.
Figu e 2 depic s each o hese ou modes. Use
A ac s in ac i e mode, use B ac s in passi e mode,
e i ie C ac s in ac i e mode, and e i ie D ac s in
passi e mode.
º
Ve i ie C
Use B
Ve i ie D
Use A
Ve i ie eques
Use esponse
Figu e 2: Sys em oles and ope a ion modes.
These modes o ope a ion a e use ul o imp o ing
p i acy in en i onmen s whe e he e a e ew de ices,
and i may be easy o de e mine hei iden i y. In his
case, he use o e i ie can go in o passi e mode and
disappea om he sys em. We will no go in o u he
de ails because i is beyond he scope o his pape .
3 CRYPTOGRAPHIC DESIGN
This sec ion desc ibes he p o ocol o use au hen i-
ca ion in a collabo a i e indoo posi ioning sys em.
3.1 P elimina ies
The symbol Hdeno es a secu e hash unc ion. We
w i e a$
←Awhen ais sampled uni o mly a andom
om A. Le edeno e a bilinea map G1×G2→GT.
3.2 P o ocol Speci ica ion
Fi s , he use mus be egis e ed in he sys em by
sending hei pe sonal in o ma ion o he issue . The
issue gene a es he c eden ials and sends hem o he
use . The use can now legi ima ely pa icipa e in he
sys em. This algo i hm will be deno ed as Issue.
Anonymous A ibu e-based C eden ials in Collabo a i e Indoo Posi ioning Sys ems
793
When he e i ie wan s o imp o e hei posi ion,
a BLE ad e isemen packe wi h a imes amp will be
b oadcas . The nea by use s will compu e he p oo
o knowledge and ansmi i ia ano he BLE packe .
This algo i hm will be deno ed as Show.
Finally, he e i ie will ensu e h ough he p oo
o knowledge ha he use has alid c eden ials and
will use he loca ion in o ma ion o posi ion hemsel .
This algo i hm will be deno ed as Ve i y.
3.2.1 Issue
To egis e he use in he sys em and gene a e he
alid c eden ials, he use and he issue pe o m he
algo i hm shown in Figu e 3.
Use Issue
q,G1,G2,GT,e,g1,g2←G(1τ),pkI
(mID)skI= (x0,x ,xID),pkI=gx0
2
m =ww/yyyy
mID
−−−−−−−−−−−−−−−−−−−−→
σ=g
1
x0+m x +mIDxID
1σx0←σx0
σx ←σx
σxID ←σxID
σ,σx0,σx ,σxID
←−−−−−−−−−−−−−−−−−−−−
S o e: σ,σx0,σx ,σxID
Figu e 3: De ini ion o he Issue algo i hm.
• The use U pe o ms he ollowing s eps:
1) In oduces pe sonal in o ma ion in he app.
2) Es ablishes a secu e communica ion channel
wi h I and sends mID.
• The issue I pe o ms he ollowing s eps:
1) Gene a es he use ’s p i a e keys x and xID.
2) Signs he a ibu es m and mID wi h he is-
sue ’s sec e key as σ=g
1
x0+m x +mIDxID
1; and
compu es auxilia y alues σx0,σx ,σxID , whe e
σx0←σx0,σx ←σx , and σxID ←σxID .
3) Sends σand auxilia y alues σx0,σx ,σxID o
he use U.
3.2.2 Show and Ve i y
To b oadcas he loca ion in o ma ion and he p oo
o knowledge, and subsequen ly e i y ha i comes
om a legi ima e use , he use and he e i ie will
un he algo i hms shown in Figu e 4.
• The e i ie V pe o ms he ollowing s eps:
1) Gene a es a nonce based on he cu en ime.
2) C ea es a BLE ad e ising packe wi h he
nonce and b oadcas s i .
Use Ve i ie
q,G1,G2,GT,e,g1,g2←G(1τ),pkI
λ= (al i ude,longi ude,la i ude,...)m =ww/yyyy
imes amp
←−−−−−−−−−−−−−−−−−−
ρ,ρκ,ρ ,ρID
$
←Z∗
q
ˆ
σ←σρ,ˆ
σx0←σρ
x0
ˆ
σx ←σρ
x ,ˆ
σxID ←σρ
xID
κ←gρκ
1σρIDρ
xID
e←H( κ,ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID , imes amp,λ)
sκ←ρκ+eρ
sID ←ρID −emID
ψ←(ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID )
π←(e,sκ,sID)ψ,π,λ
−−−−−−−−−−−−−−−−−→
0
κ←gsκ
1ˆ
σ−e
x0ˆ
σ−em
x ˆ
σsID
xID
e?
=H( 0
κ,ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID , imes amp,λ)
e(ˆ
σx0,g2) = e(ˆ
σ,pkI)
Figu e 4: De ini ion o he Show and Ve i y algo i hms.
• Nea by use s uipe o m he ollowing s eps a e
hey ha e ecei ed he imes amp:
1) Checks ha he imes amp gene a ed as a nonce
by he e i ie is less han 2 seconds om he
cu en ime o a oid eplay a acks.
2) Gene a es he andomize s ρ,ρκ,ρ ,ρID.
3) Compu es ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID , whe e ˆ
σ←σρ,
ˆ
σx0←σρ
x0,ˆ
σx ←σρ
x , and ˆ
σxID ←σρ
xID .
4) Compu es he a ibu e p oo o knowledge κ
as κ←gρκ
1σρIDρ
xID .
5) Calcula es he c yp og aphic hash eas
H( κ,ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID , imes amp,λ)and he
auxilia y p oo o knowledge alues sκ,sID,
whe e sκ←ρκ+eρand sID ←ρID −emID.
6) C ea es a BLE ad e ising packe wi h he lo-
ca ion in o ma ion λand he p oo o knowl-
edge ψ←(ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID ),π←(e,sκ,sID),
and ansmi s i by b oadcas .
• Nea by e i ie s iexecu e he ollowing s eps a -
e ecei ing ψ,π, and λ.
1) Recompu es he a ibu e p oo o knowledge 0
κ
as 0
κ←gsκ
1ˆ
σ−e
x0ˆ
σ−em
x ˆ
σsID
xID .
2) Calcula es he c yp og aphic hash using 0
κ
as H( 0
κ,ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID , imes amp,λ)and
checks i i ma ches he alue o e.
3) Compu es he bilinea pai ing e(ˆ
σx0,g2) =
e(ˆ
σ,pkI) o e i y he c eden ials we e emi ed
by he issue .
3.3 Blue oo h In eg a ion
The p oposed scheme ansmi s in o ma ion using
BLE ad e ising packe s. Blue oo h 4.2 and ea lie
SECRYPT 2021 - 18 h In e na ional Con e ence on Secu i y and C yp og aphy
794
de ined a payload size o 31 by es o a single BLE
ad e isemen packe . Howe e , since i is imp ac i-
cal o pack bo h he posi ioning da a and he p oo o
knowledge in o 31 by es, we ha e conside ed e sion
5.0 o he BLE p o ocol. Blue oo h 5.0 in oduced
a signi ican imp o emen by inc easing he capaci y
o ad e ising packe s. Wi h Low-Ene gy Ad e ising
Ex ensions, he ad e isemen payload can hold up o
254 by es (Blue oo h SIG, 2019).
To build he s uc u e o he BLE ad e ising
packe , we ha e assumed he s uc u e depic ed in
Figu e 5.
01 2 345 6 78910 11 12 13 14 15
UUID
ψ←(ˆ
σ,ˆ
σx0,ˆ
σx ,ˆ
σxID )
120B
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
ψ
12B
π←(e,sκ,sID)
92B
λ
22B
Figu e 5: De ini ion o he BLE ad e ising payload.
The UUID ield occupies 8 by es, he p oo o knowl-
edge (ψ,π) consis s o 224 by es, and he e is a ee
space o 22 by es o he posi ioning da a (λ). This
pa is explained in de ail in Sec ion 5.
4 SECURITY ANALYSIS
The p o ocol is composed o he ollowing pa s:
he anonymous c eden ials scheme, he e oca ion
scheme and he posi ioning in o ma ion. In his sec-
ion we p o ide a b ie in o mal secu i y analysis o
each o hem.
4.1 Anonymous C eden ials
Following he secu i y model de ined by (Chase e al.,
2014) o anonymous c eden ial schemes, i is e-
qui ed o mee he ollowing p ope ies:
•Co ec ness: hones use s can p oduce an accep -
ing p oo .
•Un o geabili y: dishones use s canno p oduce an
accep ing p oo .
•Anonymi y: use s canno be iden i ied based on
he alues o a ibu es.
•Key-Pa ame e Consis ency: e e y public key has
a dis inc p i a e key.
Based on he andom O acle model in (Camenisch
e al., 2019), he c eden ial scheme used in ou sys em
has p o en o be secu e unde he n-SCDHI assump-
ion (de ined below).
De ini ion 1 (n-S ong Compu a ional Di ie-Hell-
man In e sion P oblem (SCDHI)).Le Obb(·)on in-
pu (m1,...,mn)∈Z∗
q
nadd (m1,...,mn) o Q and ou -
pu g1/(x0+∑n
i=1ximi). Le Odhi(·)on inpu h ou pu hxi.
De ine he ad an age o Aas ollows.
Ad n−SCDHI(A) = P h(G,g,q)←G oupSe up(1κ),
(x0,...,xn)$
←Z∗
q
n+1,(y,m∗
1,...,m∗
n)←
AObb(·),Odh0(·),...,Odhn(·)(g):y=g
1
x0+∑n
i=1xim∗
i∧
(m∗
1,...,m∗
n/∈Qi.(1)
SCDHI is ( ,ε)-ha d i no - ime ad e sa y has ad-
an age a leas ε.
4.2 Re oca ion Scheme
Following he secu i y model de ined by (Camenisch
e al., 2016), i is equi ed o mee he ollowing p op-
e ies:
•Re oca ion Comple eness: un e oked use s will
pass he e oca ion check.
•Re oca ion Soundness: e oked use s will no
pass he e oca ion check.
•Re oca ion P i acy: use s will no lose p i acy by
p o ing an un e oked e oca ion handle.
The e oca ion scheme is based on he epoch’s ex-
pi a ion. In ou solu ion, we se he epoch o one
week and de ine he e oca ion a ibu e as ollows:
m ←ww/yyyy. When he c eden ials expi e, he use
mus enew hem, allowing weekly access con ol.
We assume ha all use s in he sys em ha e he
da e co ec ly se on hei de ices. When a use em-
po a ily swi ches o he e i ie ole, hey can p oduce
he e oca ion a ibu e wi hou equi ing he use o
disclose i .
4.3 Loca ion In o ma ion
The posi ioning in o ma ion is he c i ical componen
o he sys em. We ou line he esis ance o he p o-
ocol agains some o he mos common a acks ha
a ec he in eg i y and con iden iali y.
Ea esd opping A ack: A audulen use could
moni o he communica ions and a emp o de-
anonymize a legi ima e use because he in o ma ion
is sen in plain ex . Cap u ing communica ions is
possible since he in o ma ion is eely ansmi ed.
Howe e , emo ing anonymi y and a emp ing o link
a speci ic use o posi ioning da a is ex emely di i-
cul . Each ime a use ansmi s he posi ion, he c e-
den ials a e andomized.
Anonymous A ibu e-based C eden ials in Collabo a i e Indoo Posi ioning Sys ems
795

Replay A ack: A malicious use could ca y ou
his a ack because he in o ma ion is no al e ed.
Bu a e wo seconds, he e i ie ansmi s a new
imes amp, in alida ing he packe ’s au hen ica ion.
Du ing e i ica ion wi h he new imes amp, e?
=
H(..., imes amp,...)will p oduce a di e en alue
and he e i ica ion will ail.
Spoo ing A ack: A dishones use could a emp o
impe sona e a legi ima e use and y o p o ide ake
in o ma ion o he sys em. This a ack is imp ac ical
because a use wi hou alid c eden ials will be unable
o au hen ica e he da a.
Tampe ing A ack: A malicious use could a emp
o modi y an au hen ica ed packe o al e he posi-
ioning o use s. This a ack is un easible because in
case λis modi ied, e?
=H(...,λ)will p oduce a di -
e en alue and he e i ica ion will ail.
5 IMPLEMENTATION RESULTS
In his sec ion, we p esen he esul s o he imple-
men a ion o ou p o ocol on di e en sma phones.
Table 1 shows he ha dwa e and so wa e speci ica-
ions o he de ices used.
Table 1: HW and SW speci ica ions o he sma phones.
De ice CPU OS Blue oo h RAM
Samsung Galaxy
S21+ 5G Exynos 2100 And oid 11 5.0 LE 8 GB
Samsung Galaxy
S20 FE Exynos 990 And oid 10 5.0 LE 6 GB
Samsung Galaxy
A52 SDM720G And oid 11 5.0 LE 6 GB
Samsung Galaxy
A32
MTK D720 Dual
+ Hexa And oid 11 5.0 LE 4 GB
Samsung Galaxy
S8 Exynos 8895 And oid 9 5.0 LE 4 GB
We ha e used ellip ic cu e c yp og aphy o he im-
plemen a ion and design o he p o ocol. The im-
plemen a ion is based on he mcl c yp og aphic li-
b a y (Shigeo, 2018). I allows us o c ea e po able
applica ions be ween di e en de ices and ope a ing
sys ems and suppo s he op imal A e pai ing o e BN
cu es. We use he 256-bi Ba e o-Naeh ig cu e
(BN254) p o ided by he lib a y and compiled i
using OpenSSL (The OpenSSL P ojec , 2003) and
GMP (G anlund, 2014) as dependencies. We ob-
se ed in (Hajny e al., 2018) ha he GMP lib a y
achie es he bes pe o mance esul s o bilinea pai -
ing ope a ions. Wi h his cu e size, an uncomp essed
poin occupies 64 by es and a comp essed poin 33
by es. The size o a scala in ege is 32 by es. To
educe he size o he in o ma ion, we ha e consid-
e ed ansmi ing he poin s in hei comp essed o m.
Fu he mo e, we used he OpenSSL lib a y o com-
pu e c yp og aphic hashes. In pa icula , he SHA-2
unc ion wi h a diges size o 224 bi s.
We ha e implemen ed he p o ocol in C o mea-
su e he pe o mance on a Raspbe yPi 4. The execu-
ion on his de ice is in he o de o µs. The sma -
phone applica ion has been de eloped in Ja a and
Ko lin. The And oid NDK (Na i e De elopmen Ki )
allows us o implemen pa s o ou app in na i e code,
using languages such as C and C++. This allows us o
call he mcl lib a y unc ions h ough he Ja a Na i e
In e ace (JNI).
Finally, we benchma k he en i e p o ocol wi hou
including he communica ion o e head o e alua e he
pe o mance and speed o he algo i hms. The esul s
o he execu ion a e shown in Figu e 6. We can see he
execu ion o bo h p o ocols akes sligh ly mo e han
10 ms on he slowes de ice. Du ing he de elopmen
we used he Ene gy P o ile o And oid S udio and
did no de ec an ene gy consump ion impac .
Show Ve i y
0
2
4
6
8
1.21
2.88
1.78
3.66
2.87
6.96
3.11
7.26
3.57
7.64
Time [ms]
S. Galaxy S21+ 5G S. Galaxy S20 FE
S. Galaxy A52 S. Galaxy A32
S. Galaxy S8
Figu e 6: Speed compa ison o he Show and Ve i y algo-
i hms.
6 CONCLUSION
Ou solu ion allows sha ing anonymous loca ion in-
o ma ion in CIPSs using BLE ad e isemen , p o id-
ing eal p i acy in a ully decen alized sys em whe e
sou ces o da a can be us ed. No wi hs anding he
ela i ely limi ed implemen a ion on cons ained de-
ices, his wo k o e s aluable insigh s in o he se-
cu i y and pe o mance o implemen ing anonymous
ABC schemes on CIPSs. As a as we know, we
p esen he i s ully decen alized scheme unning
o e BLE. Ou app oach has p o en o be e icien on
SECRYPT 2021 - 18 h In e na ional Con e ence on Secu i y and C yp og aphy
796
mobile de ices and comple ely easible o eal- ime
en i onmen s. Nex , we plan o imp o e he p o ocol
o educe he size o he c yp og aphic pa , imp o e
he e oca ion scheme, p o ide in o ma ion enc yp-
ion, and s a deploymen in eal en i onmen s.
ACKNOWLEDGMENT
The au ho s g a e ully acknowledge unding om
Eu opean Union’s Ho izon 2020 Resea ch and In-
no a ion p og amme unde he Ma ie Sklodowska
Cu ie g an ag eemen No. 813278 (A-WEAR, h p:
//www.a-wea .eu/) and om Minis y o he In e-
io o he Czech Republic unde g an VJ01030002.
J. To es-Sosped a acknowledges unding om IN-
SIGNIA p ojec ( e . PTQ2018-009981, MICINN).
REFERENCES
A aoui, G., Lalande, J.-F., T ao ´
e, J., Desmoulins, N.,
Be hom´
e, P., and Gha ou , S. (2015). A p ac ical se -
membe ship p oo o p i acy-p ese ing NFC mobile
icke ing. P oceedings on P i acy Enhancing Tech-
nologies, 2015(2):25–45.
Ba ki, A., B une , S., Desmoulins, N., and T ao ´
e, J.
(2016). Imp o ed algeb aic MACs and p ac ical
keyed- e i ica ion anonymous c eden ials. In P o-
ceedings o he 2016 Selec ed A eas in C yp og aphy
- SAC 2016.
Blue oo h SIG (2019). Co e speci ica ion 5.2. Technical
Repo 5.2, Blue oo h Special In e es G oup.
B ands, S. A. (2000). Re hinking Public Key In as uc u es
and Digi al Ce i ica es: Building in P i acy. MIT
P ess, Camb idge, MA, USA.
Camenisch, J., D ij e s, M., Dzu enda, P., and Hajny, J.
(2019). Fas keyed- e i ica ion anonymous c eden-
ials on s anda d sma ca ds. In IFIP In e na ional
Con e ence on ICT Sys ems Secu i y and P i acy P o-
ec ion, pages 286–298. Sp inge .
Camenisch, J., D ij e s, M., and Hajny, J. (2016). Scalable
e oca ion scheme o anonymous c eden ials based
on n- imes unlinkable p oo s. In P oceedings o he
2016 ACM on Wo kshop on P i acy in he Elec onic
Socie y, WPES ’16, pages 123–133, New Yo k, NY,
USA. ACM.
Camenisch, J., Kohlweiss, M., and So ien e, C. (2010).
Sol ing e oca ion wi h e icien upda e o anony-
mous c eden ials. In Ga ay, J. A. and De P isco,
R., edi o s, Secu i y and C yp og aphy o Ne wo ks,
pages 454–471, Be lin, Heidelbe g. Sp inge Be lin
Heidelbe g.
Camenisch, J. and Lysyanskaya, A. (2001). An E icien
Sys em o Non- ans e able Anonymous C eden ials
wi h Op ional Anonymi y Re oca ion, pages 93–118.
Sp inge Be lin Heidelbe g, Be lin, Heidelbe g.
Chase, M., Meiklejohn, S., and Za e ucha, G. (2014). Al-
geb aic MACs and keyed- e i ica ion anonymous c e-
den ials. In P oceedings o he 2014 ACM SIGSAC
Con e ence on Compu e and Communica ions Se-
cu i y, CCS ’14, pages 1205–1216, New Yo k, NY,
USA. ACM.
Chaum, D. (1985). Secu i y wi hou iden i ica ion: T ans-
ac ion sys ems o make big b o he obsole e. Com-
mun. ACM, 28(10):1030–1044.
Chebli, M. S., Mohammad, H., and Al Ame , K. (2019).
An o e iew o wi eless indoo posi ioning sys ems:
Techniques, secu i y, and coun e measu es. In In e -
na ional Con e ence on In e ne and Dis ibu ed Com-
pu ing Sys ems, pages 223–233. Sp inge .
Des ia i, A. R., K is alina, P., and Suda sono, A. (2017).
Secu e da a ansmission scheme o indoo mobile
coope a i e localiza ion sys em. In 2017 In e na ional
Elec onics Symposium on Enginee ing Technology
and Applica ions (IES-ETA), pages 50–56. IEEE.
G anlund, T. (2014). GNU MP: The GNU Mul iple P eci-
sion A i hme ic Lib a y. h ps://gmplib.o g.
Hajny, J., Dzu enda, P., Ricci, S., Malina, L., and V ba,
K. (2018). Pe o mance analysis o pai ing-based el-
lip ic cu e c yp og aphy on cons ained de ices. In
2018 10 h In e na ional Cong ess on Ul a Mode n
Telecommunica ions and Con ol Sys ems and Wo k-
shops (ICUMT), pages 1–5. IEEE.
Hassidim, A., Ma ias, Y., Yung, M., and Zi , A. (2016).
Epheme al iden i ie s: Mi iga ing acking & spoo -
ing h ea s o ble beacons. u l: h ps://de elope s.
google. com/beacons/eddys one-eidp ep in . pd ( is-
i ed on 06/15/2016).
Kang, J., Seo, J., and Won, Y. (2018). Epheme al id beacon-
based imp o ed indoo posi ioning sys em. Symme y,
10(11):622.
Khandke , S., To es-Sosped a, J., and Ris aniemi, T.
(2019). Imp o ing inge p in ing me hods by means
o d2d communica ion p o ocol. Elec onics, 8(1):97.
Mau z, R. (2012). Indoo posi ioning echnologies.
Geod¨
a isch-geophysikalische A bei en in de Schweiz.
Pascacio, P., Cas eleyn, S., To es-Sosped a, J., Lohan,
E. S., and Nu mi, J. (2021). Collabo a i e indoo
posi ioning sys ems: A sys ema ic e iew. Senso s,
21(3):1002.
Ringe s, S., Ve heul, E. R., and Hoepman, J.-H. (2017).
An e icien sel -blindable a ibu e-based c eden ial
scheme. IACR C yp ology eP in A chi e, 2017:115.
Shigeo, M. (2018). MCL lib a y: A po able and as
pai ing-based c yp og aphy lib a y. h ps://gi hub.
com/he umi/mcl.
The OpenSSL P ojec (2003). OpenSSL: The Open Sou ce
oolki o SSL/TLS. h ps://www.openssl.o g.
Yang, J., Poellabaue , C., Mi a, P., and Neubecke , C.
(2020). Beyond beaconing: Eme ging applica ions
and challenges o ble. Ad hoc ne wo ks, 97:102015.
Zidek, A., Tailo , S., and Ha le, R. (2018). Bell ock:
Anonymous p oximi y beacons om pe sonal de-
ices. In 2018 IEEE In e na ional Con e ence on Pe -
asi e Compu ing and Communica ions (Pe Com),
pages 1–10. IEEE.
Anonymous A ibu e-based C eden ials in Collabo a i e Indoo Posi ioning Sys ems
797