qr code generator c# dll free Lesson 1 in Visual C#.NET

Printer QR Code JIS X 0510 in Visual C#.NET Lesson 1

Lesson 1
QR-Code Generation In Visual C#.NET
Using Barcode maker for VS .NET Control to generate, create Denso QR Bar Code image in Visual Studio .NET applications.
www.OnBarcode.com
QR Code Reader In Visual C#.NET
Using Barcode scanner for .NET framework Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Selecting Protocols for VPN Access
Barcode Drawer In C#.NET
Using Barcode encoder for .NET Control to generate, create bar code image in Visual Studio .NET applications.
www.OnBarcode.com
Decode Barcode In Visual C#.NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
The initial encryption key is generated during user authentication and is periodi cally refreshed. In a PPTP packet, only the data payload is encrypted. Figure 7-4 is an example of a PPTP packet, showing the addition of headers and identifying the encrypted area.
Printing Denso QR Bar Code In .NET
Using Barcode maker for ASP.NET Control to generate, create QR Code ISO/IEC18004 image in ASP.NET applications.
www.OnBarcode.com
Creating Quick Response Code In .NET Framework
Using Barcode drawer for VS .NET Control to generate, create Quick Response Code image in Visual Studio .NET applications.
www.OnBarcode.com
Encrypted IP Header GRE Header PPP
Drawing QR Code ISO/IEC18004 In Visual Basic .NET
Using Barcode generation for .NET framework Control to generate, create Quick Response Code image in .NET framework applications.
www.OnBarcode.com
Code39 Maker In C#.NET
Using Barcode generator for .NET framework Control to generate, create Code 39 Full ASCII image in VS .NET applications.
www.OnBarcode.com
Header IP Datagram
UPC-A Supplement 5 Generator In Visual C#
Using Barcode printer for .NET Control to generate, create UPC-A image in Visual Studio .NET applications.
www.OnBarcode.com
Painting Linear In Visual C#
Using Barcode printer for .NET framework Control to generate, create 1D Barcode image in VS .NET applications.
www.OnBarcode.com
Figure 7-4
Encode PDF-417 2d Barcode In Visual C#
Using Barcode maker for .NET Control to generate, create PDF-417 2d barcode image in .NET applications.
www.OnBarcode.com
Create Postnet In C#
Using Barcode creation for .NET Control to generate, create USPS POSTal Numeric Encoding Technique Barcode image in .NET applications.
www.OnBarcode.com
Encrypted portion of PPTP frame
Decoding USS Code 39 In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
EAN13 Drawer In Java
Using Barcode printer for Android Control to generate, create EAN13 image in Android applications.
www.OnBarcode.com
L2TP/IPSec
ANSI/AIM Code 128 Scanner In C#.NET
Using Barcode reader for .NET framework Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
Barcode Creator In None
Using Barcode creation for Software Control to generate, create barcode image in Software applications.
www.OnBarcode.com
L2TP/IPSec is a combination of Microsoft PPTP and Cisco Layer 2 Forwarding protocol (L2F). Characteristics of this protocol include:
UPC A Creator In Java
Using Barcode creator for Java Control to generate, create UPC-A Supplement 5 image in Java applications.
www.OnBarcode.com
Barcode Creator In Objective-C
Using Barcode creation for iPad Control to generate, create barcode image in iPad applications.
www.OnBarcode.com
L2TP tunnels data across any network that can transport point-to-point traffic. IP, Frame Relay, and Asynchronous Transfer Mode (ATM) are examples of networks that L2TP can tunnel across. L2TP uses User Datagram Protocol (UDP) over IP messages for tunnel management. L2TP send encapsulated Point-to-Point Protocol (PPP) packets over UDP. Payloads can be encrypted and compressed. IPSec Encapsulating Security Payload (ESP) is used for encryption. IPSec ESP is detailed in RFC 3193. IPSec protection comes from an automatically generated IPSec policy that uses IPSec in transport mode. Although L2TP/IPSec provides user authentication, computer authentication is also required. Computer authentication is mutual each computer must authenti cate to the other. Computer certificates are required for computer authentication. Both client and server, or both VPN routers, must have a valid certificate. Each endpoint must be able to validate the certificate presented by the other. This can be an issue when the certificates used are signed by a different certification authority. Figure 7-5 shows an L2TP/IPSec packet that is showing the encrypted portion.
Making EAN13 In None
Using Barcode maker for Software Control to generate, create EAN 13 image in Software applications.
www.OnBarcode.com
Bar Code Reader In Java
Using Barcode Control SDK for Java Control to generate, create, read, scan barcode image in Java applications.
www.OnBarcode.com
IPSec ESP Header IPSec ESP Trailer IPSec ESP Auth Trailer
IP Header
UDP Header
L2TP Header
PPP Header
PPP Payload
Encrypted
Figure 7-5
Encrypted portion of L2TP/IPSec
7
Designing Secure Communications Between Networks
Uses for IPSec Tunnel Mode
IP security (IPSec) can be used without L2TP to create an encrypted tunnel. This option is usually used to create a secure connection with a non-Microsoft router or gateway that does not support L2TP/IPSec or PPTP technologies. Unlike L2TP or PPTP, IPSec tunnel mode does not require the validation of a user account. The following facts describe uses for IPSec tunnel mode:
IP packets can be encrypted using IPSec and tunneled across an IP network. IPSec tunnel mode can be used for a demand-dial VPN or a client/server VPN. IPSec tunnel mode is not supported for client remote access VPNs. The use of IPSec filters to select or block communications using specific protocols or ports is not supported. If an IPSec tunnel mode policy is configured on a gateway, use remote access IP filters to prevent traffic outside of the tunnel from being received or forwarded. Remote access IP filters are created from the property pages of the Routing And Remote Access General Properties pages. IPSec tunnel mode requires both endpoints to be configured with complementary rules.
See Also
For explicit instructions about how to configure an IPSec tunnel mode policy, see Microsoft Knowledge Base article 816514 How To: Configure IPSec Tunneling in Windows Server 2003 (http://support.microsoft.com/default.aspx scid=kb;en-us;816514).
Considerations for Comparing VPN Protocols
To make a decision about which VPN protocol to use, you must not only know the related characteristics and operational details of all three, you must also have a clear picture of how all three are different. Only then can you determine which of the three can be used in a specific instance, and only then can you determine which one is the best security choice for a specific VPN. As you begin to consider which VPN protocol to use, think about these things:
Encryption Considerations
Encryption considerations include:
PPTP uses MPPE for encryption. L2TP/IPSec and IPSec tunnel mode use IPSec ESP for encryption.
Lesson 1
Selecting Protocols for VPN Access
PPTP encryption begins after the PPP authentication and connection process. Therefore, the authentication process is not encrypted by MPPE. L2TP/IPSec encrypts the PPP authentication packets. This arrangement provides stronger pro tection because the authentication packet must first be decrypted before common password-cracking attacks can be used on the PPP packets.
Exam Tip
PPP authentication packets, if captured, are subject to password-cracking attacks that might be successful. PPTP provides no extra protection for these packets because the encryption of PPP packets begins after PPP connection and authentication. L2TP/IPSec does provide extra protection because the PPP authentication packets are also encrypted (because user authentication occurs after the formation of an IPSec security asso ciation). A successful attacker would have to intercept the packet, defeat the IPSec ESP encryption algorithm, and then apply the password-cracking software.
PPTP uses MMPE and RC4, while L2TP/IPSec uses either Data Encryption Standard (DES) (consisting of a 56-bit key) or 3DES (consisting of three 56-bit keys) encryption. PPTP and L2TP/IPSec require user authentication using a PPP-based authentica tion protocol. L2TP/IPSec also requires computer authentication by using certificates. By requir ing two forms of authentication, L2TP/IPSec provides a stronger authentication process. However, this requirement means that each computer must have its own computer certificate. For an implementation of client-to-server VPNs of any size, using L2TP/IPSec means you must invest in a public key infrastructure (PKI). (If the implementation is very small, you might simply purchase the computer certif icates one for each of the two site-to-site VPN computers.) PPTP does not require a certificate infrastructure. IPSec ESP requires per-packet data origination authentication, which provides proof that the data was sent by a specific computer. It also requires data integrity, which is proof that the data did not change in transit. In addition, IPSec ESP pro vides replay protection, which is protection from an attack that captures and then resends a stream of data. PPTP does not provide data origination authentication, data integrity, or replay protection. IPSec ESP and PPTP (by using MPPE) provide per-packet data confidentiality (encryption).
7-10
Copyright © OnBarcode.com . All rights reserved.