You can download the full resolution file here.
Archive for the ‘security’ Category
Apple’s recently released iOS 4 provides enhanced “data protection”, but there is very little on the web now that explains what this really means. In this post I clarify what data protection is and what some of its limitations are.
What Data Protection Is
First of all, it’s important to note what encryption capability the iPhone already had (which I discussed here. The release of the iPhone 3GS (and later iPod Touch 3rd Generation) brought hardware-based full disk encryption (FDE) to the iPhone. This was designed to accomplish one thing: instantaneous remote wipe. While the iPhone 3G had to overwrite every bit in flash memory (sometimes taking several hours), disk wiping on the 3GS worked by simply erasing the 256-bit AES key used to encrypt the data.
Unfortunately, disk encryption on the iPhone did little beyond enabling remote wipe. Mobile forensicator Jonathan Zdziarski found that the iPhone OS automatically decrypts data when a request for data is made, effectively making the encryption worthless for protecting data.
So I was curious to learn what encryption improvements were made in iOS 4. Apple calls its new encryption scheme “data protection”, a substantial improvement in security design. Data protection has the primary advantage of using the user’s passcode or password to derive a key that is used to encrypt data on the device. When the phone is locked or turned off, the key is immediately erased, making data secured on the device inaccessible.
Limitations of Data Protection
The details of how data protection works are described in Apple’s recently released videos from its world-wide developers conference (see Session 209 “Securing Application Data”). This information is protected by an NDA, but I’ll summarize at a high level five basic limitations.
First, to make data encryption work a user must have an iPhone 4, iPhone 3GS, or iPod Touch 3rd Gen (previous iPhones don’t support hardware encryption). Importantly, 3GS users who upgrade to iOS must restore the device as the iOS 3 file system doesn’t support the new data protection scheme. The steps to do this are described here.
Second, files are encrypted individually by software classes that implement data protection. This means that developers must deliberately choose to use data encryption in their apps, otherwise data is unprotected. Currently, Apple says that so far only Mail is setup to use data encryption, although they say they will eventually bring data encryption to other applications. This means that even with data encryption enabled, text messages, contacts, photos, web history—in short, everything else—is left unprotected.
Fourth, to mitigate the threat of a brute force attack, the file encryption requires a key generated by the device itself, in addition to the key derived from the user’s password. This slows brute forcing because the encryption key generation process is slow by design: the iPhone 4 takes about 50 milliseconds to derive the key once the user submits a password. This means an attacker can guess only about 20 passwords per second.
This might not sound like much of a speed reduction, but this actually compares well with software-based encryption products. By comparison, I’ve used AccessData’s Password Recovery Toolkit to guess up to 900,000 passwords a second for encrypted Microsoft Office files. Encrypted PGP files allow about 900 password guesses per second.
Fifth, a weakness in the data protection system is something called the “Escrow Keybag”, which is a collection of keys necessary to decrypt every file on the device without requiring the user’s password. This was done to allow computers to sync with the iPhone without asking the user for the password.
This was a deliberate trade-off to enhance user experience. Apple’s rationale was that if the PC containing the escrow keybag was obtained, an attacker most likely already had the user’s important data anyway. For forensicators, this means that if a user’s computer is obtained along with the iPhone, it will be much easier to decrypt the user’s protected data.
Updated August 6, 2010: Elcomsoft has announced that its iPhone Password Breaker tool can recover iPhone keychains (probably the escrow keybag) from password-protected iPhone backups.
Currently, data protection in iOS 4 is still limited. Apps must be updated to use data protection and currently only Mail does so. All other data can be easily obtained without the users password.
Even so, data protection in iOS 4 represents a significant improvement over encryption in iOS 3. It is clear that Apple is striving to iteratively improve security on the iPhone, which is a good thing.
In the meantime, it looks like forensicators won’t have to worry too much about getting the data they need off of an iPhone.
I’ve wanted to install a solid-state drive (SSD) in my laptop for some time because of the dramatic boost in performance and responsiveness. However, I’ve been reluctant to buy one because I use full disk encryption (FDE) on my laptop, and I wasn’t sure how it would affect the speed of the SSD.
Unfortunately, there is not a lot of concrete information on the Web for the impact of FDE on SSD’s other than this gloomy blog post from November 2009. The author of this post used Utimaco Safeguard Enterprise to encrypt a Intel X25-M G2 160Gb SSD in a Dell Latitude E6400. Disappointingly, he found that with FDE, the SSD performed as slow or slower than the same laptop with an encrypted conventional hard drive. Clearly, in this scenario, there is little benefit to justify the cost of an SSD.
However, I use PGP 10 Whole Disk Encryption (WDE), one of the leading disk encryption products, which has just been updated with better support for SSD’s. I finally decided to purchase an SSD, and since I can’t find any other benchmarks for encrypted SSD online, I decided to perform my own.
I have a Macbook Pro 17″ (Core 2 Duo; late 2009). It used to have a Seagate Momentus 7200 RPM drive, one of the faster conventional laptop hard drives on the market, and, as stated above, it was encrypted with PGP 10 WDE. As a baseline, I used Xbench to test how fast the drive performed.
Here are its scores:
Xbench Disk Test score: 36.64
Uncached Write 73.59 45.18 MB/sec [4K blocks]
Uncached Write 52.87 29.91 MB/sec [256K blocks]
Uncached Read 37.01 10.83 MB/sec [4K blocks]
Uncached Read 67.64 33.99 MB/sec [256K blocks]
Uncached Write 9.65 1.02 MB/sec [4K blocks]
Uncached Write 81.84 26.20 MB/sec [256K blocks]
Uncached Read 69.42 0.49 MB/sec [4K blocks]
Uncached Read 72.43 13.44 MB/sec [256K blocks]
I also performed some practical, “real-use” tests as follows:
Opening iTunes: 17 seconds
Opening Papers (PDF manager): 45 seconds
Opening VMWare Fusion and resuming a Windows XP VM with 512MB RAM: 50 seconds
Opening Microsoft Word: 24 seconds
Opening PASW 17 (SPSS): 24 seconds
Copying a 5.73 GB bzip file from one part of the hard drive to another: 4 minutes, 25 seconds.
Boot time from when the PGP passphrase is typed in to the OS X login screen: 1 minute, 16 seconds.
Login time from inputing password to when the Dock appears: 20 seconds
All told, it took 2 minutes, 34 seconds to boot and load my start-up applications so I could begin using my computer normally.
The Unencrypted SSD
For comparison, I replaced the Seagate Momentus with a Crucial RealSSD, which as of April 2010, is one of the fastest SSD’s available.
Here are the same tests performed with the Crucial RealSSD unencrypted:
Xbench Disk Test score: 300.13
Uncached Write 254.02 155.97 MB/sec [4K blocks]
Uncached Write 216.33 122.40 MB/sec [256K blocks]
Uncached Read 95.35 27.91 MB/sec [4K blocks]
Uncached Read 373.91 187.93 MB/sec [256K blocks]
Uncached Write 1278.14 135.31 MB/sec [4K blocks]
Uncached Write 406.00 129.98 MB/sec [256K blocks]
Uncached Read 1578.45 11.19 MB/sec [4K blocks]
Uncached Read 947.85 175.88 MB/sec [256K blocks]
Dramatically faster. Here are some real-use comparisons:
Opening iTunes: 3 seconds
Opening Papers: 7 seconds
Opening VMWare Fusion: Loading Windows XP from suspend, 512MB RAM—7 seconds
Opening Word: 6 seconds
Opening PASW: 8 seconds
Copying the same 5.73 GB bz2 file: 52 seconds (five times faster than the encrypted hard drive).
Booting was as follows:
Boot time from Apple logo to the OS X login screen: 24 seconds.
Login time from inputing password to when the Dock appears: instantaneous
Time for start-up applications (Things, Skype, and Snapz Pro X) to load after inputing login password: 4 seconds.
The Encrypted SSD
Now with the tests of the encrypted hard drive and unencrypted SSD as baselines, I fully encrypted the 256 GB SSD using PGP 10 WDE. The process took two hours (which was in itself remarkably fast). Once the encryption process completed, I rebooted and ran the same tests again.
Xbench Disk Test score: 103.12
Uncached Write 78.22 48.03 MB/sec [4K blocks]
Uncached Write 65.20 36.89 MB/sec [256K blocks]
Uncached Read 47.00 13.75 MB/sec [4K blocks]
Uncached Read 83.05 41.74 MB/sec [256K blocks]
Uncached Write 370.32 39.20 MB/sec [4K blocks]
Uncached Write 120.49 38.57 MB/sec [256K blocks]
Uncached Read 1562.82 11.07 MB/sec [4K blocks]
Uncached Read 222.46 41.28 MB/sec [256K blocks]
As expected, the SSD is substantially slower using PGP WDE. However, it is still much faster than the encrypted 7200 RPM drive. Importantly, the uncached read times are still much faster (between 3 to 22 times faster). Probably for this reason, the user interface still feels very responsive and applications still open very quickly, with little perceptive difference from the unencrypted SSD:
Opening iTunes: 3 seconds
Opening Papers: 10 seconds
Opening VMWare Fusion—Loading Windows XP from suspend, 512MB RAM: 10 seconds
Opening Word—7 seconds
Opening PASW—9 seconds
Boot time was slower than the unencrypted SSD:
Boot time from when the PGP passphrase is typed in to the OS X login screen: 46 seconds.
Login time from inputing password to when the Dock appears: instantaneous
Time for start-up applications (Things, Skype, and Snapz Pro X) to load after inputing login password: 6 seconds.
However, when writing a large file to the disk it was painfully evident that the SSD was much slower in its encrypted state. As before, I copied the same 5.72 GB file:
Copying the same 5.73 GB bz2 file—3 minutes, 49 seconds seconds (three minutes slower than the unencrypted SSD, only a minute faster than the 7200 RPM hard drive).
Using PGP WDE 10, the SSD is still substantially faster than an encrypted 7200 RPM drive, especially for disk reads. For many tasks, the laptop still feels very fast and responsive (except when large files are written to disk). Therefore, there is value in going from an encrypted 7200 RPM drive to an encrypted SSD—the encrypted SSD is markedly faster.
However, it’s clear that the encrypted SSD is much slower than in its unencrypted form (by as much as two thirds, going by the overall Xbench score). By analogy, encumbering the SSD with FDE is like harnessing a champion racehorse to a plow. However, if you are interested in FDE, security is probably more important to you than raw speed anyway.
Update May 18, 2010:
The above tests show performance before and after encryption for the SSD, but not for the 7200 RPM drive. Robert Silvers, of Photomosaic.com, kindly provided these test results of his Seagate Momentous 7200 RPM drive before and after encrypting with PGP:
Xbench Version 1.3
System Version 10.6.3 (10D2094)
Physical RAM 4096 MB
Drive Type ST9500420ASG
Disk Test 41.56
Uncached Write 121.18 74.40 MB/sec [4K blocks]
Uncached Write 130.87 74.05 MB/sec [256K blocks]
Uncached Read 73.57 21.53 MB/sec [4K blocks]
Uncached Read 144.78 72.77 MB/sec [256K blocks]
Uncached Write 7.78 0.82 MB/sec [4K blocks]
Uncached Write 139.43 44.64 MB/sec [256K blocks]
Uncached Read 79.93 0.57 MB/sec [4K blocks]
Uncached Read 126.19 23.41 MB/sec [256K blocks]
With PGP FDE:
Disk Test 43.85
Uncached Write 69.96 42.96 MB/sec [4K blocks] (42% decrease)
Uncached Write 56.13 31.76 MB/sec [256K blocks] (57% decrease)
Uncached Read 47.55 13.92 MB/sec [4K blocks] (35% decrease)
Uncached Read 67.69 34.02 MB/sec [256K blocks] (56% decrease)
Uncached Write 12.67 1.34 MB/sec [4K blocks] (63% increase)
Uncached Write 93.32 29.87 MB/sec [256K blocks] (33% decrease)
Uncached Read 80.85 0.57 MB/sec [4K blocks] (0% change)
Uncached Read 80.05 14.85 MB/sec [256K blocks] (37% decrease)
About a 46% average loss in performance for 256K blocks.
And here are the results of the same drive using CheckPoint FDE 3.3 for Mac:
Disk Test 41.89
Uncached Write 65.65 40.31 MB/sec [4K blocks]
Uncached Write 43.13 24.40 MB/sec [256K blocks]
Uncached Read 38.09 11.15 MB/sec [4K blocks]
Uncached Read 99.15 49.83 MB/sec [256K blocks]
Uncached Write 11.57 1.22 MB/sec [4K blocks]
Uncached Write 136.74 43.78 MB/sec [256K blocks]
Uncached Read 82.63 0.59 MB/sec [4K blocks]
Uncached Read 96.35 17.88 MB/sec [256K blocks]
The results overall are slightly slower than those for PGP.
One of the new iPhone 3GS features that has received little attention this week is hardware encryption. However, from a forensics standpoint, this is probably the most significant feature of the new update. The feature is buried at the bottom of this “more features” page:
Phil Schiller also briefly mentions this feature at 1:52 of the Apple keynote.
Why Encryption on the iPhone Matters
Encryption on the iPhone matters to businesses because the iPhone can store potentially sensitive information. Among other things, forensics investigators can recover the following from iPhones (from iPhone Forensics by Jonathan Zdziarski):
- Keyboard caches containing usernames, passwords, and nearly everything typed on the iPhone.
- Screenshots of the last state of an application before the home button is pressed to return to the main menu.
- Deleted images.
- Deleted calendar entries and contacts.
- A record of the last 100 calls made.
- Viewed Google Maps images and directions.
- Browser history and caches, even when deleted.
- Deleted email messages.
- Deleted voicemail.
- Pairing records establishing which computers the iPhone was synced with.
You might think that extensive forensics experience and knowledge of the iPhone operating and file system is needed to recover this data. However, several specialized forensics tools, such as Paraben‘s Device Seizure and the Sixth Legion‘s Wolf, have automated this forensics process and can recover sensitive data from iPhones in seconds.
So it is understandable that encryption on the iPhone is a highly requested feature by corporations, according to Phil Schiller. Hardware-based encryption on the iPhone could effectively nullify forensics work on the iPhone.
Remote Wipe: A Potential Weakness
According to Schiller, hardware encryption on the iPhone 3GS enables instantaneous remote wipe. Apparently, rather than overwriting every bit as does the iPhone 3G, a remote wipe on the iPhone 3GS only overwrites the hardware encryption key, rendering all data on the iPhone unintelligible. This explains why if you later recover your iPhone 3GS, you can restore your data by enabling your MobileMe account on the iPhone, which apparently downloads the hardware encryption key to the iPhone, making the data on the iPhone readable again.
Although this feature is convenient, it does pose a potential security problem. If the hardware encryption key is hidden in the iPhone file system without being encrypted itself, then a forensics investigator could find the key and decrypt data on the iPhone. And forensics tools like a faraday cage will prevent the iPhone from receiving a remote wipe command, lengthening the window to find the encryption key indefinitely.
Of course this would require specialized knowledge of the iPhone and cryptography, but that is exactly what forensics firms like Paraben and Sixth Legion have. And their expertise is encapsulated and automated in tools like Device Seizure and Wolf, extending this ability to more general users.
So while hardware encryption on the iPhone 3GS is an interesting development, unless the encryption key is itself somehow encrypted, it will be a matter of time before the forensics community learns a way to find the key and make forensic analysis of the iPhone 3GS possible.
I wrote here that I love security measures that are simple. That is, those measures that improve security but require no more (and perhaps even less) effort than not using them. Here are three more examples.
Passphrases may not be an ideal security solution, but they are more secure and easier to remember and type than typical passwords. The fact is, passwords are the most prevalent form of authentication and they are not going away soon. Passphrases, then, usefully provide a more secure, easy-to-use alternative.
A friend of mine, Dr. Mark Keith of Arizona State University, demonstrated in a scientific study that passphrases are more secure and easier to remember than typical passwords. First, he showed that because the average person’s vocabulary consists of 3,000 words (a low estimate), a five-word passphrase is stronger than an 8-letter password using alphanumeric and special characters (3000^5 > 95^8).
He also showed that passphrases, although longer than passwords, are easier to remember and easier to use than passwords. The key is writing passphrases in standard written English, or what Keith et al. call “word processing mode” (WPM). Passphrases written in this way (like the passphrase above) are not only easier to remember, but they are also significantly easier to type and result in less login mistakes.
SSH Public Key Authentication
This one is more esoteric, but for a server administrator, SSH public key authentication is the model of security through simplicity. Rather than having to remember a password to various servers, a pair of public/private key files can be used to authenticate users instantaneously. Additionally, if a SSH public key is used in place of a password, password-guessing attacks cannot be used.
Backup is not typically thought of as a security measure, but it is probably the most important means to protect data from threats, malicious or accidental. The best way to back up data is also the simplest: routinely backing up data using automatic backup software. My favorite offline backup solution is Time Machine, which seamlessly backs up everything in the background, without any user involvement. Automatic backups is probably one of the simplest measures on this list, but also likely yields the most security for data.
IT security solutions typically involve trade-offs, usually in the form of trading increased security for reduced convenience or added hassle. However, not all security measures require this trade-off.
Some solutions—aside from the initial expense in time and money to set them up—require virtually no compromise in convenience. In fact, some may even make tasks more efficient or add functionality. Below are three examples.
Passwords are not elegant. To be worth anything they must be hard to guess, which usually makes them hard to remember. To make matters worse, users are often required to change their passwords on a regular basis, like every 90 days.
But the Web is the worst part. A typical user might have 15-30 user accounts that each require a password. Perniciously, most users soon tire of mentally maintaining a portfolio of unique passwords and relent to using the same password for every web site account. It has been said that the easiest way to steal passwords is to create an online service that requires a password. Whatever password a new user submits is most likely the same password for a dozen other online services.
The way to stop this wheel of pain is to use a password manager. A password manager is software that securely stores all of your passwords. Instead of having to remember 30 or more passwords, with a password manager you only need to know one—the password that unlocks the password manager.
Because so many passwords people must remember are for web sites, the best password managers integrate with web browsers. Using a password manager, logging into a website requires no thought—a simple keystroke retrieves the password from the password safe and fills in the username and password fields. When creating a new account at a website, the password manager generates a password for you so you don’t have to waste any thought coming up with a unique, unguessable password.
My favorite password manager is 1Password for OS X. It has saved me a lot of time and grief. Life is too short to manage passwords.
Full Disk Encryption
Another elegant security solution is disk encryption, which encrypts part or all of a hard disk. It is probably the most transparent security solution on this list because aside from entering in a password, the user is unaware that data is encrypted—there is almost no perceptible slow-down in performance. And, once encrypted, you don’t have to worry about losing your hard drive or protecting certain documents. All of your data are protected all of the time. I currently use PGP Desktop 9.10 for Mac.
I’ve done a lot of traveling in the last few months and so have used a lot of public Internet access points at airports, hotels, and other locations. Public Internet access points are not always securely configured. In some hotels for example, it is possible to sniff or eavesdrop on the Internet traffic of other guests at the hotel accessing the Internet. This is an easy way to collect passwords and other information.
One elegant solution to this problem is a VPN, or Virtual Private Network. The purpose of a VPN is to create a secure connection through an untrusted network to a trusted one. For example, my VPN creates a secure, encrypted connection to Georgia State University, no matter where I am in the world. All my traffic first is sent to GSU’s network, which I trust, and from there it continues unencrypted to sites I wish to access.
A VPN is elegant because once the VPN connection is established, all traffic is encrypted seamlessly in the background. You can access the Internet as you normally would, but now all of your Internet traffic is encrypted and safe from eavesdroppers.
My favorite VPN client is Shimo. Not only does it support a wide variety of VPN types, it is dead simple. Creating a VPN connection, even with CISCO VPN’s, only takes one button click. Plus, if I suspend my laptop while a VPN connection is active Shimo will automatically create a new VPN connection when the laptop wakes.
Yesterday PGP announced the availability of their Whole Disk Encryption (WDE) product for OS X next month. Although disk encryption products for the Mac currently exist (like TrueCrypt and FileVault), these solutions only encrypt part of a hard drive, such as a user’s home directory.
Full disk encryption (which is what WDE provides), on the other hand, encrypts every bit on a hard drive—in used or free space. This is important, because forensics products such as EnCase and FTK are very good at finding traces of sensitive information in unused disk space and temporary files like the swap. With full disk encryption, EnCase and FTK are ineffective if an encrypted machine is powered off.
Another reason why PGP WDE for Mac is exciting is because PGP is a highly respected security company and it’s WDE has been tested by the National Institute of Standards and Technology (NIST) to meet its Federal Information Processing Standard 140-2 (FIPS 140-2). Both the reputation of PGP and the FIPS-140 certification indicate that encryption algorithms employed in WDE have been implemented correctly. This is crucial because even secure encryption algorithms can be easily broken if implemented poorly.
Full disk encryption is a great tool for any organization to protect sensitive information. In the next year, Georgia State University will require that PGP Whole Disk Encryption be installed on every laptop, workstation, or server that stores sensitive information. If every organization followed a similar policiy, privacy breaches would not be the almost-weekly security farce that they are today.
I have a Mac running OS X 10.5 Leopard on my home network that I have made accessible from the Internet so I can remotely access it using SSH (Secure Shell) when I am away.
However, there are many popular SSH password brute force cracking tools (such as Hydra). Below is an excerpt from /var/log/secure.log on the Internet-accessible Mac showing an obvious brute force attack:
06:15:20 sshd: Invalid user jeff from 22.214.171.124
06:15:22 sshd: Invalid user irc from 126.96.36.199
06:15:24 sshd: Invalid user list from 188.8.131.52
06:15:25 sshd: Invalid user eleve from 184.108.40.206
06:15:27 sshd: Invalid user proxy from 220.127.116.11
06:17:28 sshd: Invalid user admin from 18.104.22.168
06:17:32 sshd: Invalid user admin from 22.214.171.124
06:17:36 sshd: Invalid user admin from 126.96.36.199
06:17:39 sshd: Invalid user administrator from 188.8.131.52
06:17:43 sshd: Invalid user administrator from 184.108.40.206
06:17:46 sshd: Invalid user administrator from 220.127.116.11
06:17:49 sshd: Invalid user tads from 18.104.22.168
06:17:52 sshd: Invalid user manet from 22.214.171.124
06:17:55 sshd: Invalid user creative from 126.96.36.199
06:18:00 sshd: Invalid user manet from 188.8.131.52
What I am not showing you are hundreds of similar attempts. Further, each username login attempt repeats as many as 20 times in a row, indicating that multiple passwords are being tried.
To entirely sidestep the threat of brute force password attacks, I have disabled password logins and only allow public-key authentication. Here is how you can set this up in OS X 10.5 Leopard:
- Edit /etc/sshd_config and change the following options, removing the ‘#’ comment sign:
- Turn off Remote Login in the Sharing preference pane in System Preferences and turn it on again to restart sshd so the changes will take effect.
Now, when someone attempts to SSH to my Mac without the correct private key, she/he will see this message:
I recently read an excellent presentation (click here for the PDF) entitled “VileFault” on the cryptographic mechanics of Mac OS X’s FileVault, a disk encryption utility. This is the first independent assessment I have read of FileVault. Other blog entries about FileVault can be found here, here, and here.
FileVault is a Mac OS X disk encryption utility that encrypts a user’s entire home directory (which contains all of a users documents and files but not programs). The Enterprise and Ultimate editions of Windows Vista contain a similar program called BitLocker Drive Encryption. An excellent open source drive encryption program, TrueCrypt, also exists. I think all of these programs mark a favorable trend toward more secure mobile computing.
To summarize the presentation, FileVault can be considered secure if it is used properly. To use FileVault effectively, users must avoid three vulnerabilities. First, users should use encrypted swap files by checking the “use secure virtual memory” setting in the security system setting panel.
Second, users should disable the Safe Sleep feature in OS X. Safe Sleep, like the Windows Hibernate feature, saves whatever is in memory to disk when the laptop battery gets too low. Unfortunately, the Safe Sleep file is not encrypted, allowing others to search for sensitive information using the “strings” or other string parsing tool.
Third, like many encryption solutions, the weakest link is usually the user’s password. The best encryption in the world can’t secure against simple passwords that can be cracked by a computer program in a matter of minutes. If you use a weak password, don’t bother using FileVault or any other form of encryption.
Interestingly, developer builds of Mac OS X Leopard show that FileVault has been significantly updated. It would be interesting to see another cryptographic assessment of FileVault after Leopard is release.
This week Insecure.org released the 2006 results of the top 100 security tools survey. The survey was performed by polling 3,243 active NMAP users (one of the most popular network security programs) on their preferred security tools. Most of the tools are free and open source and many were designed for the Unix/Linux platform.
It is a curiosity that the list of top 100 security programs could easily be called the top 100 hacking programs?both security practitioners and hackers use nearly the same toolset. For this reason it is useful to peruse this list and become familiar with the more popular tools in order to understand available capabilities for ensuring/defeating system security.