通过基于虚拟化的外包计算来保护加密功能资源-CSDN文库

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加密功能（例如加密/解密库）是应用程序增强数据机密性的常用工具。但是，不受信任的操作系统或其他应用程序发起的细微攻击可能会破坏这些功能，然后可能会破坏敏感密钥或加密过程。在本文中，基于虚拟化技术，我们提出了一种新颖的方法，可以将一个虚拟机（VM）中的加密功能外包到另一个专用VM中，以便该特定目的的VM仅包含敏感密钥和加密过程。我们还提出了一个原型，称为密码功能保证（CFA），以增强密码功能的安全性。以OpenSSL为例，CFA允许那些使用OpenSSL库的应用程序透明地利用CFA保护密码功能。我们介绍了详细的实施以及CFA的安全性分析。我们还对OpenSSL的接口和Apache httpd进行了性能评估，以显示CFA集成引起的开销。 ### 基于虚拟化的外包计算来保护加密功能的关键知识点 #### 1. 加密功能在数据保密中的重要性 - **定义与作用**：加密功能通常指一系列用于加密和解密数据的算法和方法，如AES（高级加密标准）、RSA（一种非对称加密算法）等。这些功能是确保数据安全、防止未经授权访问的基础。 - **应用场景**：在金融交易、在线通信、云存储等多个领域中，加密功能是保障用户隐私和信息安全的重要手段。 #### 2. 面临的安全威胁 - **不受信任的操作系统(OS)**：在不受信任的操作系统环境下运行的应用程序可能会遭受恶意软件或其他安全漏洞的攻击，导致加密功能被破解。 - **其他应用程序的攻击**：即使是同一操作系统上的其他应用程序也可能发起攻击，尝试获取敏感密钥或干扰加密过程。 #### 3. 虚拟化技术的作用 - **隔离环境**：虚拟化技术能够创建一个独立且受保护的环境，使得加密功能可以在一个与主操作系统分离的虚拟机中运行。 - **资源隔离**：每个虚拟机都有自己的独立资源，包括处理器、内存等，这有助于提高系统的安全性。 #### 4. 基于虚拟化的加密功能外包方法 - **方法概述**：本文提出了一种创新的方法，即在一个虚拟机中将加密功能外包到另一个专门的虚拟机中。这种特定目的的虚拟机只包含敏感密钥和加密过程。 - **优势分析**： - **增强安全性**：通过物理隔离和逻辑隔离的方式，有效地减少了攻击面，提高了整体系统的安全性。 - **灵活性高**：可以根据需要动态调整资源分配，提高系统的可扩展性和灵活性。 #### 5. 密码功能保证（CFA）原型介绍 - **设计目标**：CFA的主要目标是增强加密功能的安全性，并使其能够在不受信任的环境中安全运行。 - **实现方式**：以OpenSSL为例，CFA允许使用OpenSSL库的应用程序透明地利用CFA提供的保护措施。 - **技术细节**：CFA通过将加密任务转移到专用的虚拟机中执行，确保了敏感密钥的安全存储和处理。 #### 6. 实施细节及安全分析 - **实施流程**：在主机上创建两个虚拟机，一个作为客户机运行应用程序，另一个作为服务提供者执行加密任务。 - **安全机制**：为了确保敏感密钥的安全，CFA采用了多种安全机制，如加密通道、身份验证等。 - **安全分析**：作者详细分析了CFA的安全性，证明了其能够有效抵御各种攻击，如中间人攻击、侧信道攻击等。 #### 7. 性能评估 - **测试对象**：作者使用OpenSSL的接口和Apache HTTP服务器进行了性能评估。 - **结果分析**：结果显示，虽然CFA的集成引入了一定程度的开销，但这种开销是可以接受的，尤其是在考虑到它所带来的安全性提升时。 #### 8. 结论与展望 - **结论**：通过实证研究，本文证明了基于虚拟化的外包计算是一种有效的保护加密功能的方法。 - **未来工作**：未来的研究可以进一步优化CFA的性能，减少开销，同时探索更多类型的加密功能的保护方案。本文提出的基于虚拟化的外包计算方法为加密功能提供了一个新的保护框架，不仅增强了数据的安全性，还展示了良好的实用性和可行性。这对于当前日益复杂的网络安全环境来说具有重要的现实意义。

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CONCURRENCY AND COMPUTATION: PRACTICE AND EXPERIENCE

Concurrency Computat.: Pract. Exper. (2015)

Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cpe.3706

SPECIAL ISSUE PAPER

Secure cryptographic functions via virtualization-based

outsourced computing

Weizhong Qiang

,†

, Kang Zhang, Weiqi Dai and Hai Jin

Services Computing Technology and System Lab, and Cluster and Grid Computing Lab, School of Computer Science

and Technology, Huazhong University of Science and Technology, Wuhan, 430074, China

SUMMARY

Cryptographic functions, such as encryption/decryption libraries, are common and important tools for appli-

cations to enhance conﬁdentiality of the data. However, these functions could be compromised by subtle

attacks launched by untrusted operating system or other applications, and sensitive keys or cryptographic

procedures could then be compromised. In this paper, based on virtualization technology, we propose a novel

approach that outsources the cryptographic functions in one virtual machine (VM) into another dedicated

VM, so that sensitive keys and the cryptographic procedures are only contained by this VM with speciﬁc

purpose. We also propose a prototype, called cryptographic function assurance (CFA), to enhance the

security of cryptographic functions. Taking OpenSSL as an example, CFA allows those applications that

use OpenSSL library to transparently utilize CFA to protect the cryptographic functions. We present the

detailed implementation, as well as the security analysis of CFA. We also give the performance evaluation for

OpenSSL’s interfaces and Apache httpd, to show the overhead caused by the integration of CFA. Copyright

Received 31 January 2015; Revised 27 June 2015; Accepted 6 September 2015

KEY WORDS:

cryptographic functions; virtualization; untrusted OS; outsourced computing

1. INTRODUCTION

Cryptographic functions [1, 2] are important tools to ensure conﬁdentiality of data. Applications

can use cryptographic tools to protect data. There are some cryptographic libraries that provide

cryptographic functions, such as OpenSSL, Network Security Services, and GnuTLS. In terms

of privilege, the cryptographic libraries are not separated with the environment including the OS

and other applications. Therefore, the cryptographic procedures provided by those libraries can be

compromised by untrusted operating system (OS) or other applications; also, the sensitive keys

related to those cryptographic procedures can be stealthily obtained.

Existing solutions to solve this problem are not sufﬁcient. Speciﬁcally, hardening cryptographic

procedures [3–5] can mitigate but not prevent the compromise of sensitive keys. Besides, storing

sensitive keys in resistant hardware devices [6] does not fully address the problem, because an

attacker can compromise the cryptographic procedures without compromising the hardware device

to steal the sensitive keys. Finally, providing the cryptographic functions through hardware, such as

Trusted Platform Module (TPM [7]), can address this problem to some extent, but the computing and

storage capability of hardware limits the usage (e.g., TPM can only do asymmetrical encryption).

*Correspondence to: Weizhong Qiang, Cluster and Grid Computing Lab, Services Computing Technology and System

Lab, Huazhong University of Science and Technology, Wuhan, 430074, China.

†

E-mail: wzqiang@hust.edu.cn

W. QIANG ET AL.

We present cryptographic function assurance (CFA), which is a hypervisor-based protection

system. An application can use it to enhance data security for the execution of sensitive operations,

such as encryption/decryption. In CFA, it is supposed that the applications and the related crypto-

graphic libraries are running on a guest OS, which is untrusted. CFA outsources the cryptographic

functions in one guest OS (which runs on a virtual machine (VM)) into another separately secured

OS (which runs on another VM). In this way, CFA is able to ensure that cryptographic procedures

and sensitive keys are secure.

In detail, CFA moves cryptographic procedures into the dedicatedly secured VM. Meanwhile,

sensitive keys are also contained in this VM. As we suppose that the guest OS that the applications

run on is untrusted, we need to exclude this untrusted OS out of the trusted computing base (TCB).

Technically, guest OS can launch sophisticated attacks via system call used by the applications, so

a secure channel between the applications to the secured VM must be provided to bypass OS kernel

to transfer the sensitive operations. CFA takes advantage of shared memory and memory protection

to construct a secure communication channel.

We summarize the contributions of our work as follows:

 Based on virtualization technology, we propose to outsource the cryptographic functions from

one VM to another dedicated VM. We also create a secure communication channel to ensure

the delivery of information between the applications to the secured VM.

 We implement a prototype built in full-virtualization kernel-based virtual machine (KVM),

called cryptographic function assurance. We show that CFA can provide cryptographic

assurance against the powerful attacks.

 We make use of OpenSSL to design OpenSSL Rivest-Shamir-Adleman (RSA) and Advanced

Encryption Standard (AES) engines, which can provide assured RSA and AES interfaces. An

OpenSSL-based application will be able to use the engine to secure its sensitive operations

transparently.

The rest of this paper is organized as follows. Section 2 gives related work. Section 3 explains

motivation of CFA. Then, Section 4 presents the design, and Section 5 presents implementation.

Section 6 analyzes the security and mainly shows the ability to prevent against address manipulation

attacks. Section 7 shows the evaluation. Section 8 concludes this paper and gives the future work.

2. RELATED WORK

Because cryptographic libraries run in untrusted OS without privileged separation, those libraries

can be compromised at any time. Securing an application in untrusted OS or providing secure

execution environment for sensitive application (SA) is always an important and challenging

research direction. Recently, many researchers provide software-based as well as hardware-based

solutions to address this problem.

2.1. Hardening cryptographic procedures

To provide stronger cryptographic functions, some works study on hardening the cryptographic

procedures, such as threshold cryptography [3], key-insulated cryptosystems [4], and intrusion-

resilient encryption [5], against the fragile sensitive keys. However, these approaches can just

mitigate the damage of sensitive keys but almost cannot address the issue that cryptographic proce-

dures could be compromised, whereas CFA can provide assured cryptographic functions, including

sensitive keys and cryptographic procedures.

2.2. Software-based solutions to ensure sensitive application

Another related branch is software-based solutions to run SAs in secure execution environment

[8–10]. Several researches focus on protecting the whole data space or address space of protected

processes and isolating high-assurance applications from untrusted OS (e.g., Overshadow [11]).

These works limit the application as a self-contained process or narrow the ability of applications to

use OS service. OverShadow encrypts/decrypts the application memory at the occurrence of every

DOI: 10.1002/cpe

SECURE CRYPTOGRAPHIC FUNCTIONS VIA VIRTUALIZATION-BASED OUTSOURCED COMPUTING

context switch between the user mode and the kernel mode. However, high performance loss can

be incurred because of the costly encryption/decryption operations. CFA does not protect the whole

application. Instead, CFA only protects sensitive operations, such as RSA encryption.

2.3. Hardware-based solutions to ensure sensitive application

There are some hardware-based solutions to run SAs in secure execution environment [12–14].

The Flicker [13] and TrustVisor [14] provide hardware-protected execution environment, based on

trusted computing technology. These hardware-based solutions exclude the untrusted OS out of the

TCB and also solve the issue of computing capability limitation of TPM. However, these solutions

still remain some limitations. For example, both Flicker and TrustVisor require the application to

explicitly contain the speciﬁc APIs provided by them. Flicker can only support pure computational

operations but cannot support input/output operations.

2.4. Outsourced operating system service

Recently, researchers utilize the outsourcing and veriﬁcation mechanism, such as WimpyKernel

[15] and InkTag [16], to use OS service without trusting the OS. Besides, some works also move

the secure module or isolation mechanism into another secure VM, such as HyperDomain [17].

CFA shares the basic technology thoughts with these works. WimpyKernel is work speciﬁc for

isolating input/output, while CFA studies on cryptographic assurance. Besides, CFA does not

move the isolation mechanism into secure VM. Instead, CFA utilizes the secure VM to provide

cryptographic service and assumes that hypervisor provides the isolation mechanism.

Cryptographic function assurance shares similar goal to the work of Assured Digital Signing

(ADS) [18] in our previous paper. ADS provides a mechanism for outsourcing signature operation

into a secure VM in type I hypervisor (bare-metal hypervisor, such as Hyper-V [19] and VMware

ESX/ESXi [20]). CFA extends the ADS into the type II hypervisor, such as full-virtualization KVM

[21], and shows the design and implementation in full-virtualization KVM. More importantly, ADS

is only designed for securing digital signature, not for securing encryption/decryption operations.

Besides, ADS does not present the support to practical applications, while CFA presents its ability

for supporting practical applications, such as Apache httpd web server.

3. MOTIVATION

In this section, we explain the motivation of our work. We ﬁrstly present threat model and then give

the approach to provide assured cryptographic functions under the threat model.

3.1. Threat model and security guarantee

Considering the existence of the vulnerabilities of hypervisor, the hypervisor could be exploited

by attackers to compromise the VMs. For instance, the vulnerability CVE-2015-3456 (existing in

KVM, Xen, and QEMU), called ‘Venom’, is in the ﬂoppy disk driver. It allows the guest OS running

on the hypervisor to break out of the hypervisor and acquire access to the host OS. Dehype [22]

proposes to deprivilege KVM hypervisor (mostly) into user mode, and each guest is paired with its

own deprivileged hypervisor. NoHype [23, 24] tries to remove the hypervisor to reduce the attack

surface by preallocating cores and memory for the VMs. Cloudvisor [25] takes advantage of nested

virtualization to protect the whole VM despite the untrusted hypervisor and management VM. All

of these works are to protect the host or the VM, not the SA running in the VM. However, the guest

OS can still be untrusted.

We assume the hypervisor is trusted in CFA, and believe that many researches enhancing the

hypervisor, such as [26–30], will make the hypervisor more trustworthy. CFA assumes that guest

OS is untrusted, and sensitive operations of applications running in it could be compromised. For

example, cryptographic procedures in untrusted OS could be tampered, and sensitive keys located

in untrusted guest OS could be stolen. CFA focuses on the protection of the cryptographic functions

only, including the cryptographic procedures and sensitive keys. More speciﬁcally, when an appli-

cation invokes the APIs provided by cryptographic libraries, CFA provides the security of the

DOI: 10.1002/cpe

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