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The following example creates a named key container and adds a signature key pair and an exchange key pair to the container. This example can be run without problem even if the named key container and cryptographic keys already exist.
Example C Program: Creating a Key Container and Generating Keys.; 3 minutes to read; In this article. The following example creates a named key container and adds a signature key pair and an exchange key pair to the container. This example can be run without problem even if the named key container and cryptographic keys already exist.
Note
An application should not use the default key container to store private keys. When multiple applications use the same container, one application may change or destroy the keys that another application needs to have available. It is recommended that applications use key containers that are linked to the application. Doing so reduces the risk of other applications tampering with keys that are necessary for an application to function properly.
- Chapter 2 The Data Encryption Standard (DES) As mentioned earlier there are two main types of cryptography in use today -symmet-ric or secret key cryptography and asymmetric or public key cryptography. Symmet-ric key cryptography is the oldest type whereas asymmetric cryptography is only being used publicly since the late 1970’s1.
- The full algorithm of DES is further explained in DES algorithm (Wikipedia) and 3-DES is explained in 3-DES (Wikipedia). The code only has a single dependency on config.h in the des.c source code file. You can remove this inclusion or just create a simple header file to define one or more of the configuration options that the DES source code has.
This example demonstrates the following tasks and CryptoAPI functions:
- It attempts to acquire the named key container. If the named key container does not already exist, it is created.
- If a signature key pair does not exist in the key container, it creates a signature key pair within the key container.
- If an exchange key pair does not exist in the key container, it creates an exchange key pair within the key container.
These operations only need to be performed once for each user on each computer. If the named key container and key pairs have already been created, this sample performs no operations.
This example uses the following CryptoAPI functions:
This example uses the function MyHandleError. The code for this function is included with the sample. Code for this and other auxiliary functions is also listed under General Purpose Functions.
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The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST).
DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only). General Structure of DES is depicted in the following illustration −
Since DES is based on the Feistel Cipher, all that is required to specify DES is −
- Round function
- Key schedule
- Any additional processing − Initial and final permutation
Initial and Final Permutation
The initial and final permutations are straight Permutation boxes (P-boxes) that are inverses of each other. They have no cryptography significance in DES. The initial and final permutations are shown as follows −
Round Function
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The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.
- Expansion Permutation Box − Since right input is 32-bit and round key is a 48-bit, we first need to expand right input to 48 bits. Permutation logic is graphically depicted in the following illustration −
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- The graphically depicted permutation logic is generally described as table in DES specification illustrated as shown −
- XOR (Whitener). − After the expansion permutation, DES does XOR operation on the expanded right section and the round key. The round key is used only in this operation.
- Substitution Boxes. − The S-boxes carry out the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. Refer the following illustration −
- The S-box rule is illustrated below −
- There are a total of eight S-box tables. The output of all eight s-boxes is then combined in to 32 bit section.
- Straight Permutation − The 32 bit output of S-boxes is then subjected to the straight permutation with rule shown in the following illustration:
Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration −
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The logic for Parity drop, shifting, and Compression P-box is given in the DES description.
DES Analysis
The DES satisfies both the desired properties of block cipher. These two properties make cipher very strong.
- Avalanche effect − A small change in plaintext results in the very great change in the ciphertext.
- Completeness − Each bit of ciphertext depends on many bits of plaintext.
During the last few years, cryptanalysis have found some weaknesses in DES when key selected are weak keys. These keys shall be avoided.
S-des Key Generation Code In C 1
DES has proved to be a very well designed block cipher. There have been no significant cryptanalytic attacks on DES other than exhaustive key search.