Protecting Data in the Cloud: An Assessment of Practical Digital

Envelopes from Attribute based Encryption

Victor J. Sosa-Sosa, Miguel Morales-Sandoval, Oscar Telles-Hurtado

and Jose Luis Gonzalez-Compean

Center of Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV),

Parque Cient

ıﬁco y Tecnol

ogico TECNOTAM, Km. 5.5 carretera Cd. Victoria-Soto La Marina, Ciudad Victoria, Mexico

Keywords:

Attribute-based Encryption, Cloud Storage, Security, Access Control, Conﬁdentiality, Authentication.

Abstract:

Cloud storage services provide users with an effective and inexpensive mechanism to store and manage big

data with anytime and anywhere availability. However, data owners face the risk of losing control over their

data, which could be accessed by third non-authorized parties including the provider itself. Although con-

ventional encryption could avoid data snooping, an access control problem arises and the data owner must

implement the security mechanisms to store, manage and distribute the decryption keys. This paper presents a

qualitative and quantitative evaluation of two Java implementations of security schemes called DET-ABE and

AES4SeC. Both are based on the digital envelope technique and attribute based encryption, a non-conventional

cryptography that ensures conﬁdentiality and access control security services. The experimental evaluation

was performed in a private cloud infrastructure where experiments for both implementations ran using the

same platform, settings, underlying libraries, thus providing a more fair comparison. The quantitative evalua-

tion revealed DET-ABE and AES4SeC have similar performance when applying low security levels (128-bit

keys), whereas DET-ABE surpasses AES4SeC performance when medium (192-bit keys) and high (256-bit

keys) security levels are required. Qualitative evaluation shows that AES4SeC also ensures authentication and

integrity services, which are not supported by DET-ABE.

1 INTRODUCTION

Cloud storage is one of the most demanded services

in the cloud computing model. That service is very

attractive for users because it allows the storage of a

high volume of data at a relative low cost and with the

guarantee of availability and reliability.

One of the main aspects delaying the acceptance

of cloud storage services is security (Theoharidou

et al., 2013). Data owners are often reluctant to out-

source their data to distant cloud servers because non-

authorized parties including the service provider can

learn from their data in plaintext form.

The two main security services demanded in a

cloud storage service are (Theoharidou et al., 2013;

Chow et al., 2009):

• Conﬁdentiality: Non-authorized entities can learn

anything from owners’ data.

• Fine grained access control: Data owners can se-

lectively decide who can access and use their data.

Conventional cryptography (Menezes et al., 1996)

can be used to implement some schemes that en-

sure the conﬁdentiality of data (i.e. using symmet-

ric cryptography) and the sharing of the encryption

key to consumers by means of cryptographic digital

envelopes (asymmetric encryption). However, under

this solution approach the key management is respon-

sibility of the data owner which must implement the

secure mechanisms to store and share the keys. In ad-

dition, the data owner must know the identity of con-

sumers in advance (i.e. their public key) before cre-

ating the digital envelope and sending the encrypted

key to them.

Attribute-based encryption (ABE) (Sahai and Wa-

ters, 2005) is non conventional cryptography. Instead

of using traditional keys, ABE encrypts using a pol-

icy over a set of attributes, which deﬁnes an access

control mechanism and many-to-many encryption. In

ABE, the encryptor does not need to know the identity

of data consumers in advance, it encrypts data to all

those whose attributes satisfy the encryption policy.

Consumers are provided with a set of attributes. A

key is derived from users’ attributes and used for

382

Sosa-Sosa, V., Morales-Sandoval, M., Telles-Hurtado, O. and González-Compeán, J.

Protecting Data in the Cloud: An Assessment of Practical Digital Envelopes from Attribute based Encryption.

DOI: 10.5220/0006484603820390

In Proceedings of the 6th International Conference on Data Science, Technology and Applications (DATA 2017), pages 382-390

ISBN: 978-989-758-255-4

data decryption. Only those that have the attributes

that satisfy the encryption policy will be able to de-

crypt.

ABE is considered an important enabler technol-

ogy to provide the security services demanded in

cloud storage. Nevertheless, there are few avail-

able implementation of ABE schemes for practical

use in end user applications (Zickau et al., 2016).

ABE are complex systems relying in the theory of

elliptic curves and bilinear pairings, with several as-

pects to cover for a secure and efﬁcient implementa-

tion. Most of the reported works on ABE are theo-

retical constructions, for example (Koo et al., 2013;

Saikeerthana and Umamakeswari, 2015; Fu et al.,

2014). Those works do not present experimental re-

sults that prove the schemes are well suited for use in

practice.

There are two kinds of ABE schemes: KP-ABE

and CP-ABE. In KP-ABE, the attributes are associ-

ated to the ciphertext and the access structure is as-

sociated to the keys. In CP-ABE the situation is the

opposite, the attributes are associated to decryption

keys and the access structure is associated to the ci-

phertext. This way, CP-ABE is conceptually closer to

the role based access control (RBAC) technology and

preferred for providing the access control mechanism

for data stored in the cloud.

In the same way, there are two common con-

structions of CP-ABE. The ﬁrst one is based on the

Bethencourt et al (Bethencourt et al., 2007) work,

where the access structure is implemented as a tree

(leaf nodes are attributes and internal nodes are logic

gates deﬁning the encryption policy). Some repre-

sentative ABE schemes using this type of technique

are (Bobba et al., 2009; Wan et al., 2012). DET-

ABE (Morales-Sandoval and Diaz-Perez, 2015) is a

Java application that implements this technique. The

second approach is based on the constructions given

by Waters (Waters, 2011), where the access structure

is implemented as a matrix and the encryption poli-

cies are represented as formatted boolean formulas.

Some representative constructions of ABE schemes

with matrix implementations of the access structure

are (Liu et al., 2015; Liu and Wong, 2016). AES4SeC

(Morales-Sandoval et al., 2017) is a Java applica-

tion that implements these ABE schemes. Additional

to offer conﬁdentiality and access control, AES4SeC

also provides authentication and integrity services.

This work presents a quantitative and qualitative

comparison of two realizations of CP-ABE for pro-

viding conﬁdentiality and access control mechanism

over the data stored in untrusted cloud servers. By it-

self, CP-ABE is not able to encrypt large amounts of

data. For that reason, DET-ABE and AES4SeC

implement the digital envelope technique, that uses a

symmetric cipher to encrypt data of any size, and the

decryption key is encrypted with CP-ABE, thus en-

forcing access control and conﬁdentiality at the same

time. Both schemes use the Advanced Encryption

Standard (AES) as symmetric cipher, with support of

the three security levels of 128-, 192-, and 256-bit.

An study as the one presented here allows us to

highlight the advantages and disadvantages of prac-

tical implementations of the two most representative

ABE constructions. Our results show how execution

time varies for different security level requirements

and sizes of ﬁles that are shared through a ﬁle shar-

ing system. These results can be of interest to those

users that plan to implement this kind of cryptogra-

phy in real scenarios for data storage and sharing in

the cloud.

The remainder of this paper is organized as fol-

lows: Section 2 presents the generalities of an ABE

scheme. Section 3 describes the concept of digital

envelopes and how DET-ABE and AES4SeC imple-

ments that cryptographic concept to guarantee con-

ﬁdentiality and access control mechanisms for large

amount of data. Section 4 describes the set of ex-

periments and the settings to evaluate DET-ABE and

AES4SeC under the same conditions. This section

discusses the results achieved and provides a quanti-

tative comparison. Finally, Section 5 presents the con-

clusion of this work and points out the future work.

2 ATTRIBUTE BASED

ENCRYPTION

Attribute based encryption is a relative new cryp-

tography that has a main distinctive that no keys but

policies are used for the data encryption process. A

policy is generally a boolean formula over a set of

attributes. An attribute is a property of an entity, for

example “to be a doctor”, “to have an academic

degree”, etc. For simplicity, attributes can be viewed

as text-strings. As an example consider the policy:

P = [“doctor”and“cardiologist”] or

[“nurse”and“hospital number 25”]

If P were used in ABE, the encrypted data (ciphertext)

can be only decrypted by entities having attributes

= {a

, a

, ··· , doctor, · ·· , cardiologist, · ·· } or S

, a

, · ·· , nurse, · ·· , hospital number 25, · ·· }.

In ABE, a user having the sets S

or S

will be

given a decryption key completely dependent on its

attributes. When decrypting, the decryption key will

match the policy “mathematically”. CP-ABE consists

Protecting Data in the Cloud: An Assessment of Practical Digital Envelopes from Attribute based Encryption

383

of four main algorithms:

1. setup (1

)- initializes the scheme creating a public

key PK and a master private key MK. Both keys

are derived from arithmetic over an elliptic curve

recommended for use in cryptography. The secu-

rity level is expressed in terms of n.

2. encrypt(PK, data, policy) - encrypts data using

PK and the given policy. The result is the cipher-

text CT.

3. decrypt(SK

, ciphertext) - decrypts the given ci-

phertext using the decryption key SK

of user u.

The decryption key is generated using the attribute

set assigned to u. The result is the data in plain

form.

4. keygen(S, MK) - generates a decryption key using

a set S of attributes and the master key MK.

In CP-ABE schemes, a trusted authority is in

charge of executing the algorithms setup and keygen,

and to safeguard MK. In simple terms, encryption

and decryption occur as follows (for formalisms see

(Bethencourt et al., 2007; Waters, 2011)): data D to

be encrypted is mapped to a number M in a multi-

plicative group (D 7→ M). Each attribute i in the pol-

icy is also mapped to a number C

in the form of ex-

ponentiations in a group (i 7→ C

). The ciphertext is a

set of numbers produced from a secret value s, gen-

erated internally. The SK

key is also a set of num-

bers that result from mapping each user attribute i to

an abstract number and also hiding them in the form

of exponentiations (i 7→ D

). The only way to reveal

the user attributes or the attributes in the encryption

policy is by solving the discrete logarithm problem,

which is believed to be hard for groups of large or-

der (key size). During decryption, the mathematical

processing of each component {C

, D

} associated to

attribute i allows to recover the secret s and get back

D after a series of mathematical operations.

3 SECURITY SCHEMES BASED

ON DIGITAL ENVELOPES

Digital envelopes are cryptographic objects con-

structed using public key encryption. The main pur-

pose of a digital envelope is the secure distribution

of symmetric keys (Menezes et al., 1996). Each par-

ticipant u has a pair of related keys {K

priv

, K

pub

}, with

priv

private and K

pub

public. Anyone can encrypt and

send encrypted data to u using K

pub

but only u can de-

crypt using K

priv

. The digital envelope has the main

distinctive that the data being encrypted is a symmet-

ric key k, which has been used to encrypt the real con-

tent to be shared in secret with u.

3.1 DET-ABE

Authors in (Morales-Sandoval and Diaz-Perez, 2015)

present DET-ABE (Digital Envelope Technique - At-

tribute Based Encryption), an implementation of the

digital envelope that uses the Advanced Encryption

Standard (AES) as the symmetric cipher and CP-

ABE to selectively distribute the AES key to de-

cryptors. DET-ABE encrypts for the security levels

recommended by the National Institute of Standards

and Technology (NIST): 128-bit (minimum security

level), 192-bit (medium security level), and 256-bit

(maximum security level).

In DET-ABE the user is responsible for specifying

the level of security to be applied.

The process securing data in DET-ABE is as follows:

1. Internally, an AES-key (k) is generated from a se-

curity level λ given by the user.

2. AES encrypts data using k, producing the cipher-

text CT

AES

3. Then, CP-ABE is used to encrypt k, given a policy

P over a set of valid attributes S obtaining as a

result the ciphertext CT

ABE

4. Finally, {CT

AES

, CT

ABE

} is stored in a binary ﬁle,

which can be uploaded to the cloud.

The general process of DET-ABE encryption is

shown in the Figure 1.

Figure 1: DET-ABE encryption process.

DET-ABE implement CP-ABE according to the con-

struction provided by Betancourt et al. (Bethencourt

et al., 2007), which proposed as access structure a tree

structure where its nodes represents threshold gates

(AND, OR) and the leaves describe attributes. The

AND and OR gates are constructed as n-of-n and

1-of-n threshold gates, respectively. Generalizing,

threshold gates are of the form m-of-n where m ≤ n.

KDCloudApps 2017 - Special Session on Knowledge Discovery and Cloud Computing Applications

384

Figure 2: Tree access structure of policy (B ∨C) ∧ A.

In DET-ABE each policy is represented in postﬁx no-

tation, for example:

• Attributes S = {A, B,C, D}

• Policy P as a boolean formula over S: (B ∨C) ∧ A

• P in postﬁx notation = B C 1-of-2 A 2-of-2

In the previous example, the representation of P as a

tree structure is shown in Figure 2.

3.2 AES4SeC

AES4SeC (Attribute based Encryption and Signing

for Security in the Cloud) is a Java implementation

of CP-ABE (Morales-Sandoval et al., 2017) accord-

ing to the construction provided by Waters in (Waters,

2011), which uses a matrix as access structure (for an

access policy that includes n attributes). This scheme

was designed to provide conﬁdentiality, access con-

trol and authentication in the process of storage, re-

trieval and sharing content in the cloud. AES4SeC

uses the elliptic curve a bilinear pairing setting of CP-

ABE to support digital signing using short signatures,

which only require pairing-based cryptography (at-

tributes are not used nor policies). Data is secured

in the same way than with DET-ABE but additionally

the data is digitally signed. This case, the security

level of signatures must be compliant with the one for

data encryption. Internally, digital signing hashes the

data using the Secure Hash Algorithm SHA-2 and by

a series of arithmetic operations produces the digital

signature σ. Now, what is stored in a binary ﬁle and

uploaded to the cloud is the triplet {CT

AES

,CT

ABE

, σ}.

The general process of AES4SeC signing and encryp-

tion is shown in Figure 3.

AES4SeC uses Formatted Boolean Formu-

las (FBF) to represent access policies. A For-

matted Boolean Formula can be expressed as

, F

, ..., F

,t), where n and t deﬁnes a (n,t)-gate

of the FBFs F

, F

, · ·· , F

. The value n is implicitly

decided by the number of the children, and only the

threshold value t is explicit in the formula. F

is either

an attribute or another FBF. For example,

: (A ∧ B)

as a FBF: (A, B, 2)

Figure 3: AES4SeC encryption process.

: (C ∨ D)

as a FBF: (C, D, 1)

P: (A ∧ B) ∧ (C ∨ D)

P as a FBF: (P

, P

, 2)

3.3 Qualitative Comparison

The main differences between DET-ABE and

AES4SeC include: the security assumptions in each

construction, the implementation of access structure,

the security services provided and the performance of

main operation. The ﬁrst three are summarized in Ta-

ble 1. The last one is discussed with more details in

the next section.

DET-ABE follows the construction provided by

(Bethencourt et al., 2007), which is proven to be se-

cure in the random oracle model. Contrary, AES4SeC

uses the construction given by (Waters, 2011), which

is proven to be secure in the standard model. The

security assumptions in the later are more solid, foun-

dationally sound and practical.

The access structure in DET-ABE is realized as

a tree, which can exhibit a better timing when pro-

cessed. Policies in FBF format can be more expres-

sive but the realization of the access structure as a

matrix could have penalties in the timing when pro-

cessing policies that produce a matrix of high dimen-

sion. Finally, although both DET-ABE and AES4SeC

guarantee conﬁdentiality and access control, only

AES4SeC can also guarantee integrity, authentica-

tion, and non-repudiation by incorporating the digi-

tal signature of the data at low cost, because the set-

ting for deploying ABE is reused for providing the

pairing-based cryptography that requires the digital

signature algorithm.

Protecting Data in the Cloud: An Assessment of Practical Digital Envelopes from Attribute based Encryption

385

Table 1: Comparison between DET-ABE and AES4SeC.

DET-ABE AES4SeC

Security model Random oracle Standard

Access structure Tree Matrix

Conﬁdentiality? 3 3

Access control? 3 3

Authentication? 7 3

Integrity? 7 3

Non-repudiation? 7 3

4 EXPERIMENTAL EVALUATION

The main aim of this experimentation was to evalu-

ate general features and performance of two appli-

cations that provide conﬁdentiality and access con-

trol services to digital content. This content will be

shared among users of 4 different organizations using

a ﬁle sharing system running on a private cloud en-

vironment. Each application implements DET-ABE

and AES4SeC, both running on a Java 8.0 virtual ma-

chine.

4.1 Prototype and Setup

Our interest was focused mainly on evaluating perfor-

mance of DET-ABE and AES4SeC when providing

different levels of security, such as minimum (128-

bit keys), medium (192-bit keys) and high (256-bit

keys), where one to four attributes can be involved

in the encryption policies. The evaluation was moti-

vated by the need for exchanging digital content in a

secure way among users that belong to four different

organizations by using a ﬁle sharing system that runs

on a private cloud environment. The sizes of the ﬁles

being shared in the cloud are 1KB, 1MB, 10MB and

100MB. In this scenario, we assume that the level of

sensitivity of digital content has been determined by

the content owner, as well as the level of coverage,

i.e., deﬁne the users that will be able to access the

shared content and that belong to an particular orga-

nization. For this evaluations, for simplicity we de-

ﬁned four organizations, each one represented by the

attributes A, B, C and D, respectively.

The infrastructure used in our experimentation

represents a prototype of SkyCDS (Gonzalez et al.,

2015), which is a resilient delivery service based on

diversiﬁed cloud storage. For testing purposes, we

use a program that emulates a client generating ﬁles

that are submitted in a secure way into the cloud stor-

age. This client node is a 64 bits Intel core i7, 2.5Ghz

with 8GB in RAM and 1TB of HD running Ubuntu

16.04 LTS as operating system.

Table 2 shows the details of the instances used in

SkyCDS. Nevertheless, this article only reports the

impact on the ﬁle generator node.

Table 2: Characteristics of the cloud instance.

Type # Instances Cores RAM HD

Metadata 1 2 2GB 100GB

Storage 5 4 6GB 80GB

4.2 Cryptographic Algorithms Settings

Table 3 shows the key sizes used in experimentation

for both DET-ABE and AES4SeC. NIST has recom-

mended three security levels expressed in terms of the

key size of AES. While 128-bit is intended for pro-

tecting sensible data in general purpose applications,

192-bit are for more restrictive domains, as in mili-

tary or government. The security level of 256-bit is

recommended for protecting top secret data and for

national security interests.

Digital envelopes in DET-ABE and AES4SeC use

AES together with CP-ABE. Thus, these two cryp-

tosystems must offer equivalent security strenght in

terms of keys sizes. While brute force is the best at-

tack over AES to obtain the encryption key, for CP-

ABE the attack comes by solving the discrete loga-

rithm problem over three sets: G

, G

, and G

. Key

sizes in CP-ABE are strongly related with the size of

elements in these sets. G

and G

are sets of ellip-

tic curve points deﬁned over a ﬁnite ﬁeld F

. G

is an

extension ﬁeld of F

with degree k. In this experimen-

tation we use the setting for the key sizes of CP-ABE

provided in (Morales-Sandoval et al., 2017), for type

F-curves, using an asymetric setting for the pairing

deﬁned by the mapping G

× G

7→ G

As a comparison and putting this in perspective, a

content that is secured with AES using a 128bit key

would require a key of 3072 bits to provide a similar

level of security using RSA.

4.3 Metrics and Testbech

The time required for encrypting digital content by

both applications was used as main performance met-

ric in this evaluation. It is important to recall that

the conﬁdentiality and access control services are pro-

vided by the DET-ABE and AES4SeC applications.

However, AES4SeC also provides authentication and

integrity services by including digital signing func-

tions. For a fair performance comparison between

the DET-ABE and AES4SeC applications, it was nec-

essary to switch off the digital signing functions in

AES4SeC, limiting its services only to provide conﬁ-

dentiality (AES cipher) and access control (CP-ABE

KDCloudApps 2017 - Special Session on Knowledge Discovery and Cloud Computing Applications

386

Table 3: Key sizes for different security levels. Security strength and period of protection are speciﬁed by NIST.

Security strength ζ Period of protection

Key size (bits)

AES G

128 2030-2040 128 512 1024 3072 256

192 >2030 192 1280 2560 7680 640

256 >2030 256 2560 5120 15360 1280

implementation). In order to distinguish between

the original AES4SeC application and its incomplete

version, without including integrity and authentica-

tion services, we named this version of AES4SeC as

AES4SeCi. As a ﬁrst approach, we were interested

in evaluating performance in applications providing

conﬁdentiality and access control services using a

particular CP-ABE strategy. However, after compar-

ing performance of the DET-ABE and AES4SeCi ap-

plications, we also evaluated how the digital signing

function impacts performance when running the com-

plete version of AES4SeC. This evaluation is useful

for decision makers to determine how feasible is to

include authentication and integrity services in a ﬁle

sharing system in a private cloud environment, when

using different levels of security and where different

number of attributes can be involved in the cipher

policies.

As mentioned in Section 3, DET-ABE implements

CP-ABE using an access structure over attributes in

form of a tree, where its nodes represent threshold

gates (AND, OR) and the leaves describe attributes.

For this evaluation we only used AND gates, deﬁning

the following encryption policies in postﬁx notation:

• A 1-of-1 : One attribute (A)

• A B 2-of-2 : Two attributes (A ∧ B)

• A B 2-of-2 C 2-of-2 : Tree attributes (A ∧ B ∧C)

• A B 2-of-2 C 2-of-2 D 2-of-2 : Four attributes (A ∧

B ∧C ∧ D)

In order to create the digital content used in this

evaluation, we generated a set of ﬁles of the following

sizes: 1KB, 1MB, 10MB and 100MB. Each ﬁle was

encrypted with the three security levels: minimum

(128-bit keys), medium (192-bit keys), high(256-bit

keys).

Since AES4SeC is based on the concept of For-

matted Boolean Formula (FBF), as was described in

Section 3, the four previous policies as FBF formulas

were deﬁned as following:

• F

= (A, 1)

• F

= (A, B, 2)

• F

= (A, B,C, 3)

• F

= (A, B,C, D, 4)

Similar to the DET-ABE evaluation, ﬁles of dif-

ferent sizes (1Kb, 1MB, 10MB, and 100MB) were

generated in this experiment, and every ﬁle was se-

cured considering the tree security levels (minimum,

medium and high) and every cipher policy.

The securing process for each ﬁle using every en-

cryption policy and every security level was carried

out 31 times, and the median was taken as a way to

normalize the results for DET-ABE and AES4SeC.

4.4 Performance Evaluation

This section presents a summary of the performance

evaluation carried out to DET-ABE and AES4SeC,

based on the test scenario and conﬁgurations deﬁned

in the previous section. Figure 4 shows time required

by DET-ABE to secure ﬁles of different sizes (vertical

axis), considering the four previously deﬁned policies

and minimum, medium and high security levels (hor-

izontal axis). Notations in Figure 4 should be read as

follows: <name of application>-<size of the encryp-

tion key 128,192,256>-<number of attributes con-

sidered 1A, 2A, 3A, 4A>. For instance, in Figure

4, the ﬁrst four bars grouped with the tag DETABE-

128-1A in the X axis show the time in seconds (Y

axis) required by the DET-ABE application consider-

ing a minimum (128bit key) security level and only

one attribute (1A).

0.5

1.5

2.5

1 kB

1 MB

10 MB

100 MB

Time(Sec)

Figure 4: Time required to secure ﬁles using DET-ABE.

Focusing on every security level (groups of 128bit,

192bit and 256bit key sizes), it is revealed that the

Protecting Data in the Cloud: An Assessment of Practical Digital Envelopes from Attribute based Encryption

387

number of attributes is not having a considerable im-

pact (in terms of absolute time) in DET-ABE perfor-

mance. For instance, the difference between the max-

imum and minimum time required for securing a ﬁle

of 100MB with a 192bit key using one, two, three

or four attributes is only about 9 milliseconds. For

the user perspective, this means that they will not no-

tice the difference when sharing ﬁles secured using

different encryption policies. Something similar hap-

pens with the time required to secure ﬁles whose size

is ranging from 1KB to 10MB using DET-ABE in a

particular security level. The users will not notice im-

portant differences when sharing ﬁles with this range

of size as the difference in performance is null. It is

clear in Figure 4 that, as expected, impact on perfor-

mance is observed when DET-ABE moves to a higher

security level. In this scenario, when moving from

minimum security level to medium security level a

performance degradation of about 1.5x is perceived

(e.g., 150% more time is required for securing a ﬁle

of 10MB). Moving to the next security level, from

medium to high, performance goes down about 4x,

e.g. 400% more time required for securing a ﬁle of

10MB), and it gets worst when moving from mini-

mum to high security level, decreasing more than 11x,

e.g., 1100% more time required for securing a ﬁle

of 10MB). Even though the percentage of additional

time required for securing documents with a high se-

curity level seems unfeasible, in absolute terms it will

depend on the number of ﬁles to be secured. For ex-

ample, for securing a 100MB ﬁle in a high security

level using DET-ABE with 4 attributes only requires

2.8seconds, which is a very acceptable value com-

pared with the time that will be required to transfer

the ﬁle in a commercial network; at this rate we could

secure more than 20 ﬁles per minute, which is an ac-

ceptable value for some organizations.

The next evaluation is focused on the performance

produced by AES4SeCi (AES4SeC version similar to

DET-ABE). As we can see in Figure 5, AES4SeCi

shows a very similar behavior to DET-ABE in terms

of low negative performance impact, when the num-

ber of attributes changes in a particular security level

and securing ﬁles whose size is ranging from 1KB

to 10MB. The evident negative performance impact

in a speciﬁc security level, especially in minimum

and medium, occurs when securing ﬁles of 100MB.

Notation rules in this ﬁgure are similar to those pre-

sented for DET-ABE, for instance, AES4SECi-128-

1A refers to the AES4SeCi application using a 128bit

key with one attribute.

The most important impact on performance degra-

dation produced by AES4SECi arises when moving

from lower to higher security levels. In this sense,

1 kB

1 MB

10 MB

100 MB

Time(Sec)

Figure 5: Time required to secure ﬁles using AES4SeCi.

its performance degradation is higher than DET-ABE,

for example, the performance degradation obtained

when moving from minimum to high security level

when securing a 10MB ﬁle is about 24x, it seems un-

feasible, but in absolute values it means more than 5

seconds of difference.

4.5 Comparison

Taking into account that our main interest is focused

on providing conﬁdentially and access control to a ﬁle

sharing system, where users from four different orga-

nization (or four attributes in our evaluation context)

will exchange content using different security levels,

in Figure 6, we show a comparison between DET-

ABE and AES4SeCi, both using 4 attributes imple-

menting different security levels, minimum, medium

and maximum.

As we can see, with minimum security levels and us-

ing four attributes DET-ABE and AES4SeCi show

very similar performance. This behavior changes

gradually with medium security levels and an evi-

dent difference occurs with high security levels. The

average performance degradation rate of AES4SeCi

compared with DET-ABE is about 110%, especially

in medium and high security levels. In our test sce-

nario, these results reveal that the access structures

over attributes in form of a tree implemented in DET-

ABE offer similar performance than the matrix im-

plementation and the use of the concept of Formatted

Boolean Formula (FBF) in AES4SeCi when a min-

imum security level is required. However, the tree

structures of CP-ABE implemented in DET-ABE al-

low it to improve performance in higher security lev-

els when compared with the matrix implementation

of AES4SeC.

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1 kB

1 MB

10 MB

100 MB

Time(sec)

Figure 6: DET-ABE and AES4SeCi comparison using en-

cryption policies with 4 attributes.

Since AES4SeC also provides the authentication

and integrity services, which are important security

requirements in some organizations, we carried out

an experiment to verify how these functions impact

in the performance of AES4SeC, running the incom-

plete (AES4SeCi) and complete (AES4SeC) versions

of AES4SeC on the same previous scenario using en-

cryption policies with four attributes.

1 kB

1 MB

10 MB

100 MB

Time(Sec)

Figure 7: Impact of signing functions in AES4SeC.

Figure 7 reveals that the degradation impact in perfor-

mance of the signing functions of AES4SeC is almost

null when minimum security levels are used. The

largest impact occurs in high security level with 27%

of performance degradation, which occurs when se-

curing ﬁles of 100MB. This results are still encourag-

ing for organizations requiring all of the security ser-

vices (conﬁdentiality, access control, authentication

and integrity services).

5 CONCLUSION

This paper presented useful insights on performance

of two Java applications, DET-ABE and AES4SeC,

which implement different CP-ABE strategies to pro-

vide conﬁdentiality and access control security ser-

vices. These two applications offer a Java program-

ming interface that hides the complexity of imple-

menting encryption policies and Attribute-Based En-

cryption (CP-ABE) algorithms, security parameters

and type and size of elliptic curves needed for mini-

mum (128-bit key), medium (192-bit key) and max-

imum (256-bit key) security levels, making simple

their use and inclusion as building blocks in end user

applications. AES4SeC also provides authentication

and integrity services, for a fair comparison these

functions were switch off, named this incomplete ver-

sion AES4SeCi. Experiments carried out on DET-

ABE and AES4SeCi showed that the impact on per-

formance is almost null when the number of attributes

change in the encryption process, when a particular

security level is applied. However, they suffer an ev-

ident performance impact when moving from low to

high security levels. An interesting ﬁnding was that

the two applications showed very similar performance

when securing ﬁles of 1KB, 1MB and 10MB and

100MB using a minimum security level. However

AES4SeCi showed lower performance when medium

and high security levels were applied, almost dou-

bling the time required for securing the same group

of ﬁles. In general terms, results revealed that the

CP-ABE implementation in DET-ABE, based on tree

structures, improves performance of the matrix im-

plementation made in AES4SeCi, which is based on

the concept of Formatted Boolean Formula (FBF).

It is worth recalling that the complete version of

AES4SeC also provide integrity and authentication

services, in this sense, experiments showed that im-

pact on performance of its signing functions is almost

null when a minimum security level is used, and time

required to secure the same group of ﬁles in medium

and high security levels (less than 5 and 6 seconds re-

spectively in average), represents an attractive option

for users demanding secure ﬁle sharing with integrity

and authentication functionalities.

ACKNOWLEDGEMENTS

This work was partially supported by the sectoral fund

of research, technological development and innova-

tion in space activities of the Mexican National Coun-

cil of Science and Technology (CONACYT) and the

Mexican Space Agency (AEM), project No.262891.

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389

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