## 数学代写|密码学作业代写Cryptography代考|CRN15668

statistics-lab™ 为您的留学生涯保驾护航 在代写密码学Cryptography方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写密码学Cryptography代写方面经验极为丰富，各种代写密码学Cryptography相关的作业也就用不着说。

## 数学代写|密码学作业代写Cryptography代考|BOOLEAN Encoding

We start with the first ASN.1 types in the order of their type values. Fortunately for us, that means BOOLEAN is the first type, which is also the simplest to deal with.
The length determination function is fairly trivial.
der_boolean_length.c:
001 unsigned long der_boolean_length (void)
002 f return 3;
003 ;
004 }
der_boolean_length.c:
001 unsigned long der_boolean_length(void)
002 {
003 return 3 ;
$004 \quad}$
As we can see, this function has only four lines. All BOOLEAN encodings are three bytes long regardless of whether they are true or false. It is important to note that the length determination functions can fail. In such cases, we will use zero length as our error indicator. In the case of BOOLEAN, all inputs are valid.
der_boolean_encode.c :
001 #include “asn $1 . h$ “
002 int der_boolean_encode(int bool,
003 unsigned char *out,
004 unsigned long *outlen)
005{
$006 /$ /* check output size */
007 if (der_boolean_length() > *outlen) {
008 return -1 ;
$009}$
010
$011 /$ * store header and length */
013
$014 \quad / *$ store payload */
$015 \quad$ *out $=($ bool $==0)$ ? $0 \times 00: 0 \times 0 F$;
016
$017 / *$ finished ok */
018 return 0 ;
$019}$

## 数学代写|密码学作业代写Cryptography代考|INTEGER Encoding

Encoding an integer is fairly straightforward when the numbers are positive. In the case of positive numbers, the encoding is simply the byte encoding of the integer stored in big endian format. For negative numbers, we need to be able to find a power of 256 larger than the absolute value and encode the sum of the two.
The ASN.1 specification does not put a small limit on the size of the integer to be encoded. So, long as the length can be encoded (less than 128 bytes of length), the integer is within range. However, at this point we do not have any way of dealing with large integers. Therefore, we are going to artificially limit ourselves to using the C long data type. The reader is encouraged to take note of the limited functionality required to properly support the INTEGER type.
Before we get into encoding and decoding, we must develop a few helper functions for dealing with integers. These functions are commonplace in the typical large number library and trivial to adapt.
int help.c:
001 #include “asn $1 . \mathrm{h}$ “
002
003 int count bits(long num)
004{
005 int $x$;
$006 \mathrm{x}=0$;
007 while (num) ${++\mathrm{x}$; num $\gg=1 ;}$
008 return $\mathrm{x}$;
$009}$

This function returns the number of bits in the integer. It assumes the integer is positive (or at least not sign extended) and simply shifts the integer right until it is zero.
011 int count_lsbs(long num)
012{
013 int $\mathrm{x}$;
$014 \mathrm{x}=0$;
015 if (Inum) return 0 ;
016 while $(1$ (num\& 1$)) \quad{++\mathrm{x} ;$ num $\gg=1 ;}$
017 return $\mathrm{x}$;
$018}$

# 密码学代写

## 数学代写|密码学作业代写Cryptography代考|BOOLEAN Encoding

der_boolean_length.c:
unsigned long (void)
002 f return 3;
003;
004}
der_boolean_length.c:
unsigned long (void)
002年{
003返回3;
004美元\四}

der_boolean_encode.c:

002 int der_boolean_encode(int bool;
003 unsigned char *out，
004 unsigned long *outlen)
005年{
$006 /$ /检查输出大小/
007 if (der_boolean_length() > *outlen) {
008返回-1;
009美元}
010
$011 /$ *存储头和长度*/
013
$014 \quad / *$ store payload */
$015$ *out $=($ bool $==0)$ ?$0 \乘以00:0 \乘以0 F$;
016
$017 / *$ finished ok */
018返回0;
019美元}

## 数学代写|密码学作业代写Cryptography代考|INTEGER Encoding

ASN.1规范对要编码的整数的大小没有小的限制。因此，只要长度可以被编码(长度小于128字节)，该整数就在范围内。然而，在这一点上，我们没有任何处理大整数的方法。因此，我们将人为地限制自己只使用C long数据类型。鼓励读者注意正确支持INTEGER类型所需的有限功能。

int help.c:

002
003 int count bits(long num)
004年{
int $x$;

007 while (num) ${++\ mathm {x}$;Num $\gg=1;}$
008返回$\ mathm {x}$;
009美元}

int count_lsbs(long num)
012年{
013 int $\math {x}$;

015 if (Inum)返回0;

MAC输出的长度。正如我们在6.3.3节中讨论的，可以只使用HMAC输出的一部分作为实际MAC，但是减少它的长度会降低安全性。

## 有限元方法代写

tatistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。

## 数学代写|密码学作业代写Cryptography代考|Different levels of data integrity

statistics-lab™ 为您的留学生涯保驾护航 在代写密码学Cryptography方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写密码学Cryptography代写方面经验极为丰富，各种代写密码学Cryptography相关的作业也就用不着说。

## 数学代写|密码学作业代写Cryptography代考|Different levels of data integrity

Data integrity is a slightly confusing security service because it is often referred to in different contexts. The best way of identifying the context is to consider the strength of a potential ‘attack’ against the integrity of some data. For our purposes, we will consider four different levels of data integrity which can be provided by considering four increasing levels of attack:

Accidental errors. This first level of data integrity provides protection only against accidental errors. Such errors are most likely to occur through noise in a communication channel. Data integrity mechanisms offering this level of data integrity include error-correcting codes (see Section 1.4.4) and simple checksums such as cyclic redundancy checks (CRCs). These techniques involve the computation of a digest which is appended to the original data. The digest is computed using a simple mathematical computation based on the data. Since the digest can be computed by anyone, these mechanisms offer no protection against an active attacker. We will not further discuss mechanisms in this category, since their integrity protection is weak.

Simple manipulations. The second level of data integrity protects against simple manipulations. Mechanisms providing protection only against accidental errors often have the property that if the data is changed in a particular way, then the new integrity digest can be predicted without needing to formally recalculate it. For example, the integrity digest of the XOR of two messages might be the XOR of the two integrity digests. Hash functions are examples of mechanisms which can protect against simple manipulations, since they have inherent security properties which can detect such manipulations. However, an active attacker can still defeat integrity mechanisms in this category since the integrity digest can still be computed by anyone. This second category is only distinct from the first category in that an active attacker cannot ‘shortcut’ the computation of a new digest by manipulating old ones. We will discuss hash functions in Section 6.2.

Active attacks. The third level of data integrity protects against active attacks. Unlike the previous two categories, mechanisms in this category must be able to prevent an attacker from creating a ‘valid’ integrity digest on some data for which they have not previously seen an integrity digest. This strong notion of data integrity normally requires data origin authentication, since the most natural way of preventing active attacks of this type is to provide a binding between the underlying data and the source creating it. The main cryptographic mechanisms for providing this level of data integrity are MACs, which we discuss in Section 6.3.

## 数学代写|密码学作业代写Cryptography代考|Hash functions

Hash functions are probably the most versatile of all cryptographic primitives. They are extremely useful and appear in all sorts of surprising applications. As a stand-alone tool, they have few uses. However, no cryptographic designer should ever leave home without one! Such is their ubiquity that when an unexpected attack was announced in 2004 against several of the most widely deployed hash functions, there was considerable concern. Their many important and varied uses include:

As strong one-way functions. Hash functions are sometimes used to ‘encrypt’ highly confidential data which does not require ‘decryption’, such as passwords (see Section 6.2.2).

To provide a weak notion of data integrity. Hash functions can be used to provide checks against accidental changes to data and, in certain cases, deliberate manipulation of data (see Section 6.2.2). As such they are sometimes referred to as modification detection codes or manipulation detection codes.

As components to build other cryptographic primitives. Hash functions can be used to construct different cryptographic primitives such as MACs (see Section 6.3.4) and digital signature schemes with appendix (see Section 7.3.4).

As a means of binding data. Hash functions are often used within cryptographic protocols to bind data together in a single cryptographic commitment.

As sources of pseudorandomness. Hash functions are sometimes used to pseudorandomly generate numbers for use in cryptography, with an important example being the generation of cryptographic keys (see Section 10.3).

Note the term hash function has several other wider meanings in the field of computer science. While we will use the term hash function because our context is clear, our hash functions are sometimes more specifically referred to as cryptographic hash functions.

# 密码学代写

## 有限元方法代写

tatistics-lab作为专业的留学生服务机构，多年来已为美国、英国、加拿大、澳洲等留学热门地的学生提供专业的学术服务，包括但不限于Essay代写，Assignment代写，Dissertation代写，Report代写，小组作业代写，Proposal代写，Paper代写，Presentation代写，计算机作业代写，论文修改和润色，网课代做，exam代考等等。写作范围涵盖高中，本科，研究生等海外留学全阶段，辐射金融，经济学，会计学，审计学，管理学等全球99%专业科目。写作团队既有专业英语母语作者，也有海外名校硕博留学生，每位写作老师都拥有过硬的语言能力，专业的学科背景和学术写作经验。我们承诺100%原创，100%专业，100%准时，100%满意。

## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。