Securing Applications and Data · ⁨การป้องกันแอปพลิเคชันและข้อมูล⁩

Learning Objective 5.2.A: Explain how the state or classification of data impacts the type and degree of security applied to that data.

• 5.2.A.1 Organizations implement specific security controls to comply with legal requirements based on the types of data they collect, store, process, and transmit.
• 5.2.A.2 Data can be classified by their state.
  • Data at rest are stored on a drive. It is important to protect the physical drive storing the data from destruction or theft. Data at rest can also be encrypted so that if an adversary steals it, they can’t immediately read the data.
  • Data in transit are being sent from one device to another. If the data are being transferred over physical media (e.g., cables) it is important to protect the media. Data in transit can also be encrypted so that if an adversary intercepts it, they can’t immediately read the data.
  • Data in use are being processed by software or a person. Access controls can be used to limit who or what has the ability to use data in different ways (e.g., view or edit). Data must be unencrypted to be used.
• 5.2.A.3 Organizations often categorize data according to their sensitivity and prioritize a higher degree of security for more sensitive information.
• 5.2.A.4 Laws and regulations can require certain types of data to be stored, transmitted, and handled according to specific rules.
  • Personally identifiable information (PII) is any data that allows someone to be identified and includes (but is not limited to): name, signature, phone number, address, biometric data (e.g., fingerprints), social security number, date of birth, and email address. The protection of this data is covered by many laws but most notably The Privacy Act of 1974 and for children under the age of 13 the Children’s Online Privacy Protection Act of 1998.
  • Protected health information (PHI) is any data related to an individual’s health, treatment, payment for healthcare at any time and includes (but is not limited to): test results, treatment records, hospital records, doctor visit notes, and health provider payment records. The protection of PHI is included in the Health Insurance Portability and Accountability Act of 1996.
  • Payment card information (PCI) is the data collected by organizations to process payments via cards (e.g., credit cards) and includes the following: name, account number, expiration date, address, and CVV code. The protection of this data is regulated by the Payment Card Industry Data Security Standard (PCI-DSS).
• 5.2.A.5 Organizations that collect regulated data will label them and have policies that comply with the legal or regulatory requirements for the safe storage, transmission, and handling of these data.

Learning Objective 5.2.B: Identify managerial controls related to application and data security.

• 5.2.B.1 A cryptography policy will describe the acceptable encryption protocols and key parameters for an organization and may include:
  • A list of encryption algorithms approved for specific uses
  • Minimum or maximum key lengths
  • Cryptographic key-generation requirements and parameters
  • Cryptographic key-storage requirements
• 5.2.B.2 A web application security policy will outline the requirements and parameters for testing and mitigating web application vulnerabilities in an organization, and it may include:
  • Parameters for when an application is subject to a security assessment
  • Timelines for remediating vulnerabilities based on level of risk
  • Parameters for how an application security assessment is to be carried out (e.g., using specific tools or according to specific frameworks)

Learning Objective 5.2.C: Determine an appropriate access control model to protect applications and data.

• 5.2.C.1 Access control enforces which users or applications (called subjects) can access, modify, add, or remove (called operations) which files or applications (called objects). Access control models describe how to determine which subjects have what type of access to which objects.
• 5.2.C.2 Role-based access control (RBAC) assigns every subject to a role and defines which roles have which types of access to which objects.
  • Illustrative examples for 5.2.C.2:
    • An example of a role at a company might be “accountant,” and one type of object could be the payroll software. Role-based access could be used to ensure that only subjects who are assigned to the role of “accountant” have access to the payroll software object.
• 5.2.C.3 Rule-based access control (RuBAC) checks a set of rules to determine what type of access a subject should have for a specific object and then allows or denies types of access based on the rules. This access control model is typically layered on top of another access control model.
  • Illustrative examples for 5.2.C.3:
    • There is a rule that prohibits subjects (even those who would normally have access) from accessing a certain database (the object) outside of local working hours. When a subject attempts to access the database, even if they are authorized to access it, they will be denied access if it is outside the time designated by the rule.
• 5.2.C.4 Discretionary access control (DAC) gives individual subjects the ability to set the type of access that other subjects have on objects they own. In DAC models some subjects are designated as administrators or super users, and they have the ability to override the access controls established by other subjects.
  • Illustrative examples for 5.2.C.4:
    • Bob creates a file (an object) and decides to give Alice permission to edit the file, to give Frank permission to view the file only, and to deny everyone else access to the file altogether.
• 5.2.C.5 Mandatory access control (MAC) follows strict rules for which types of access each subject level has for objects that are above their level, at their level, or below their level. Subject and object levels are assigned by an external administrator.
• 5.2.C.6 The Bell-LaPadula model is a MAC model that is often used by governments and military organizations to control the security of information. This model has the following two important properties:
  • i. The Simple Security Property states that subjects may not read objects that are above their level.
  • ii. The * (Star) Security Property states that subjects may not write to objects below their level.
  • These rules taken together are often summarized as “write up, read down” (WURD).
• 5.2.C.7 The principle of least privilege is the idea that entities should be given exactly as much access as they need to perform their function and no more.

Learning Objective 5.2.D: Configure access control settings on a Linux-based system.

• 5.2.D.1 Authorization is when an entity is granted permission to have a certain type of access to a resource. Access controls are put in place to control which users have what types of access to which data.
• 5.2.D.2 There are three types of access to a file in Linux that can be set, and they always come in the following order:
  • i. Read access allows a user to view the contents of a file.
  • ii. Write access allows a user to make changes to a file.
  • iii. Execute access allows a user to run a binary file such as a program.
  • These are abbreviated rwx, respectively. If a user only has read and execute permissions (not write), then it would display as r-x. The - symbol indicates the absence of that permission.
• 5.2.D.3 There are three default entities for which permissions are set and always in this order: (1) the file owner, (2) the file group, and (3) all other users. The three sets are displayed with no spaces (e.g., rwxrwxrwx).
• 5.2.D.4 To view the current permission settings for a file, use the command ls -l, which will show the current settings for the default entities. If there is a + symbol at the end of the permissions, this means that other permissions have been set for that file and it can be viewed with the getfacl command.
• 5.2.D.5 To modify the permission settings for a file, use the chmod command. This command can be used with the numeric method or the symbolic method.
• 5.2.D.6 To use chmod in the numeric method the syntax is chmod ### filename. Each of the three ### represents one of the three entities mentioned above (the owner, the group, other nongroup users).
  • The first # = the owner
  • The second # = the group
  • The third # = other nongroup users
  • The permission for each entity is determined by adding up the values for the types of access to be granted:
  • 0 = no permissions
  • 1 = execute
  • 2 = write
  • 4 = read
  • Therefore 3 sets permission to write and execute, 5 sets permission to read and execute, 6 sets permission to read and write, and 7 sets permission to read, write, and execute.
  • Illustrative examples for 5.2.D.6:
    • The command chmod 750 test would set the permissions for the owner to read, write, and execute, for the group to read and execute, and for everyone else to no access at all.
    • The command chmod 543 test would set the permissions for the owner to read and execute, for the group to read only, and for everyone else to write and execute.
    • The command chmod 777 test would set the permissions for all three entities to read, write, and execute for the file test.
• 5.2.D.7 To use chmod in the symbolic method the syntax is chmod entity +(or –) permission filename. The entities are the user owner, the group, and other nongroup users. Each entity is represented with a single letter.
  • u = user owner
  • g = group
  • o = others
  • a = all
  • Permission can be either added or removed to any combination of entities.
  • • = add the permission
  • – = remove the permission
  • The permissions that can be set are read, write, and execute.
  • r = read
  • w = write
  • x = execute
  • Entities and permissions can be combined in a single command. To add the read and execute permissions for the group and user owner for a file called testfile, the command would be chmod ug+rx testfile.

Learning Objective 5.3.A: Explain how encryption can be used to protect files.

• 5.3.A.1 The purpose of cryptography is to hide information. A cryptographic algorithm defines a process for encrypting and decrypting information. Encryption is the process of hiding the information, and decryption is the process of reversing the encryption to retrieve the original information.
• 5.3.A.2 An encryption algorithm defines a process for combining the information to be encrypted with a predefined key. The information to be encrypted is called the plaintext. The output of the encryption algorithm is called the ciphertext.
• 5.3.A.3 The number of possible keys that can be used in an encryption algorithm is called the keyspace. The larger the keyspace, the longer it will take an adversary to discover the correct key by random chance.
• 5.3.A.4 Cryptographic algorithms are classified by whether they use one key or two keys.
  • Symmetric encryption algorithms use the same key to encrypt and decrypt information.
  • Asymmetric encryption algorithms use two different keys—one to encrypt information and the other to decrypt information.
• 5.3.A.5 Cryptographic algorithms are also classified by whether they process information one bit at a time or in fixed-size chunks of bits.
  • Block encryption handles information in fixed-size chunks called blocks, producing an output block for each input block.
  • Stream encryption handles input information continuously, producing output one element at a time.

Learning Objective 5.3.B: Apply symmetric encryption algorithms to encrypt and decrypt data.

• 5.3.B.1 Computer-based encryption algorithms operate on binary data. The most common symmetric encryption algorithm is the Advanced Encryption Standard (AES). AES encryption is used to secure Wi-Fi transmissions, internet browsing, file encryption on disks, and hardware-level encryption on processors.
• 5.3.B.2 AES is a symmetric key block cipher that encrypts data in 128-bit blocks (16 bytes). AES can operate with keys of varying lengths. Longer keys produce more secure encryption but require more time to encrypt and decrypt.
• 5.3.B.3 Symmetric encryption and decryption can be performed using the command line, specialized software, or web-based tools.
  • On a command line interface, users can encrypt or decrypt with OpenSSL.
  • Specialized software like AES Crypt is an open source tool that can encrypt and decrypt files.
  • There are many web-based tools for encrypting and decrypting files.
• 5.3.B.4 Using OpenSSL in a CLI, a user can encrypt and decrypt a file using the following commands (note that the encryption key is derived from the password provided):
  • To encrypt a file named test with AES using a 128-bit key, use the command: openssl enc -aes-128-cbc -e -in test -k password -out test.enc
  • To decrypt the encrypted file using the same key, use the command: openssl enc -aes-128-cbc -d -in test.enc -k password -out text

Learning Objective 5.4.A: Determine the appropriate asymmetric key to use when sending or receiving encrypted data.

• 5.4.A.1 Asymmetric encryption allows users to communicate securely without prearranging a shared secret key.
• 5.4.A.2 When using asymmetric encryption, each entity that will be receiving data must first generate a key pair. Key pairs are binary strings of equal length that are generated at the same time through a mathematical process. One key is designated as the public key and the other as the private key. The keys are mathematical inverses of each other— each key reverses its partner. Either key can be used to encrypt information, but only the other key in the key pair will then be able to decrypt it.
• 5.4.A.3 Once the receiver generates the key pair, the private key must be stored securely. If the private key is exposed, shared, stolen, corrupted, or compromised the key pair must be deleted and a new key pair must be generated, because the security of the encryption algorithm rests on the security of the private key. The public key is published for anyone to view and use.
• 5.4.A.4 To send information securely to someone, the sender will use the receiver’s public key to encrypt the data and send it. Only the receiver who has the private key will be able to decrypt and read the information.

Learning Objective 5.4.B: Explain why the length of a key impacts the security of encrypted data.

• 5.4.B.1 Longer keys result in larger keyspaces. For binary keys, an n-bit length key has a keyspace of $2^n$.
• 5.4.B.2 Using an application to randomly guess an n-bit length encryption key means that on average an adversary will be able to guess the correct key in $2^n \div 2$ (or $2^{n-1}$) guesses.
• 5.4.B.3 Although longer keys are more secure, they also require more time to encrypt and decrypt messages.
• 5.4.B.4 Computational processing power and efficiency continue to improve, allowing software to guess keys faster. Key-length recommendations for both symmetric and asymmetric encryption algorithms are periodically increased to account for increased processing power.
• 5.4.B.5 Key-length comparison is only valid when comparing keys for the same cryptographic algorithm.
  • Illustrative examples for 5.4.B.5:
    • An AES 256-bit key is more secure than an AES 128-bit key.
    • An RSA 4096-bit key is more secure than an RSA 2048-bit key.
    • RSA and AES keys cannot be directly compared to one another in determining the level of security.

Learning Objective 5.4.C: Apply asymmetric encryption algorithms to encrypt and decrypt data.

• 5.4.C.1 Common asymmetric encryption algorithms include RSA and elliptic curve cryptography (ECC). Asymmetric algorithms are used in many applications, including digital signatures and digital certificates.
• 5.4.C.2 As with symmetric encryption, asymmetric encryption and decryption can be performed using the command line, specialized software, or web-based tools.
  • On a command line interface, users can encrypt or decrypt with OpenSSL.
  • Specialized software like RSA Encryption Tool is an open source tool that can encrypt and decrypt files.
  • There are many web-based tools for encrypting and decrypting files.
• 5.4.C.3 In a CLI, a user can generate an asymmetric key pair and encrypt or decrypt files as necessary.
  • To generate a 2048-bit RSA key pair and save the key to a file named rsa.pem use the command: openssl genrsa -out rsa.pem 2048
  • To extract the public key from rsa.pem into a file named public.pem, use the command: openssl rsa -pubout -in rsa.pem -outform PEM -out public.pem
  • To encrypt the file test using RSA encryption and the key file public.pem, use the command: openssl pkeyutl -encrypt -pubin -inkey public.pem -in test -out test.enc
  • To decrypt the test.enc file using the rsa.pem file, run the command: openssl pkeyutl -decrypt -inkey rsa.pem -in test.enc -out test

Learning Objective 5.5.A: Identify the application security principles of secure by design and security by default.

• 5.5.A.1 Secure by design is an initiative that encourages companies to include security in all phases of product development including design. When organizations implement secure by design, security is a design principle not just a technical feature.
• 5.5.A.2 Secure by design includes three design principles:
  • i. Companies should take ownership of customer security outcomes. Companies should build products that meet the security needs of their customers.
  • ii. Companies should embrace radical transparency and accountability. Sharing relevant security-related product news and updates quickly increases security for everyone.
  • iii. Companies should build organizational structure and leadership to implement secure by design. Companies need leaders who are focused on security and have a security-first posture.
• 5.5.A.3 Secure by design includes the concept of secure by default, which is the idea that security features for software and devices should be enabled by default. Devices and software should be secure to use out of the box, with security features already enabled.

Learning Objective 5.5.B: Explain how user input sanitization protects applications.

• 5.5.B.1 When users enter input into an application, the application typically encases that input in special characters to process it. The characters that encase the user input are called control characters and include the single quote, the double quote, and the semicolon.
• 5.5.B.2 When creating a program that takes user input, programmers should use a function to verify that user input meets their expected criteria and does not include any control characters that could be used to manipulate the system. This verification function can sanitize user input by removing potentially malicious characters, or it can give the user an error and force the user to provide different input. This can protect against many application attacks, including:
  • SQL injection attacks
  • XSS attacks
  • Directory traversal attacks

Learning Objective 5.6.A: Explain how to detect attacks on data.

• 5.6.A.1 Devices track and log when data are accessed and by whom. The process of recording and monitoring user activities is called accounting. Analysis of these logs can reveal malicious activity when an adversary attempts to access, copy, move, or delete data. Suspicious activity can include:
  • Accessing files that aren’t typically accessed
  • Accessing files or applications outside of a user’s normal patterns (including time of day, location, and device type)
  • Attempts to delete or copy sensitive files
• 5.6.A.2 A honeypot is a file that appears as if it contains valuable data (e.g., credit card information, PII, passwords), but the data in the file are fake. A system can alert defenders if someone attempts to access the honeypot. Since the honeypot is a fake file, there is no legitimate reason to be accessing it, and any attempted access would be an indicator of malicious activity.
• 5.6.A.3 Cryptographic hash functions can generate a digest for data and can reveal if data have been altered. If a file has changed unexpectedly, this can be a sign of malicious activity.

Learning Objective 5.6.B: Determine controls for detecting attacks against applications or data.

• 5.6.B.1 Cost is a criterion in determining detective controls. Detective controls like honeypots and using hash values to check data integrity are inexpensive. Some organizations invest in third-party data loss prevention (DLP) services, which monitor data access, usage, and transmission by users throughout the organization to detect suspicious activity; DLP services provide strong detection capabilities at a higher cost.
• 5.6.B.2 Sensitivity or criticality of data or applications is a criterion in determining detective controls. More sensitive or critical data or applications are more likely targets of an adversary and should be monitored more closely.
• 5.6.B.3 Classification of data is a criterion in determining detective controls. Data that have been classified as private, educational, healthcare, or financial often have legal or regulatory detection and monitoring requirements.

Learning Objective 5.6.C: Evaluate the impact of a method for detecting attacks against an application or data.

• 5.6.C.1 To operate at an effective speed, log analysis needs to be augmented with some automation. Honeypots offer near instantaneous detection capabilities.
• 5.6.C.2 Some DLP tools, honeypots, and realtime automated log analysis provide alerts as an attack is happening. These tools allow for a prompt response that can stop an attack before it does more harm. Retrospective log analysis and the use of cryptographic hashes to verify data integrity identify attacks after they have occurred.
• 5.6.C.3 False negatives can occur in applications and data attack detection. Cryptographic hash functions only detect if data have been altered. An adversary could view and steal data without altering it, and a cryptographic hash function would not detect this. Honeypots cannot detect adversaries that do not attempt to access them.

Learning Objective 5.6.D: Identify whether a file has been altered by verifying its hash.

• 5.6.D.1 Cryptographic hash functions can help identify changes in a file because they are repeatable: the same input always produces the same output for a given hash function.
• 5.6.D.2 Hashes can be calculated using the command line on a computer, a website, or specialized software.
  • In Windows Powershell, if a user wanted to generate the SHA256 hash for a file named testfile, they would use the command: Get-FileHash testfile -Algorithm SHA256
  • In BASH the same could be accomplished with the command: sha256sum testfile
  • In zsh, the common command line terminal on Apple computers, this could be accomplished with the command: shasum -a 256 testfile
• 5.6.D.3 A file can be hashed and its hash output recorded. Then it can be hashed again later, and the second hash output can be compared to the previous hash output for the same file. If a file’s hash changes, then the file was altered between when the first and second hashes were generated.

Learning Objective 5.6.E: Apply detection techniques to identify and report indicators of application attacks by analyzing log files.

• 5.6.E.1 SQL injection attacks can be detected by reviewing application and server logs of user input for SQL control words and symbols such as:
  • A single (') or double (") quote character
  • Boolean conditions like OR 1=1
  • A double dash (which indicates a comment in SQL): --
  • SQL control words (always in capital letters) like WHERE, IN, FROM
• 5.6.E.2 XSS attacks can be detected by reviewing user input for suspicious tags, particularly the tag.
• 5.6.E.3 For web applications, buffer overflows can be detected by checking the amount of data the user is sending to the web application in their request. The fields commonly checked are the URL length, cookie length, query string length, and total request length. Long strings in any of these fields can be an indicator of an attempted buffer overflow attack.
• 5.6.E.4 Directory traversal attacks can be detected by reviewing application and server logs. HTTP GET requests that include paths with sequences of ../ are indicators of an adversary attempting a directory traversal.