What Is a Scintigraphy?

Cryptography is a technical science that studies the preparation and decoding of passwords. The study of the objective law of cryptographic changes, applied to the preparation of passwords to keep communication secrets, is called coding; those applied to deciphering passwords to obtain communication information, is called deciphering, collectively known as cryptography. The telegraph was first invented by Morse in the United States in 1844, so it is also called Morse code. It consists of two basic signals and different intervals: a short point signal ".", Read "" (Di); a long signal that stays for a certain time "-", read "answer" (Da). Interval time: tick, 1t; answer, 3t; tick, 1t; letter, 3t; word, 5t.

Cryptography

Cryptography is a technical science that studies the preparation and decoding of passwords. The study of the objective law of cryptographic changes, applied to the preparation of passwords to keep communication secrets, is called coding; those applied to deciphering passwords to obtain communication information, is called deciphering, collectively called cryptography. The telegraph was originally from the United States

Cryptography (in

Cryptography (in

In the communication process, the information to be encrypted is called plaintext, the encrypted information is called ciphertext, and only the information known to both the sender and the sender is called the key. Under key control, the process of changing from plain text to cipher text is called encryption, and the reverse process is called de-encryption or decryption. In the password system, in addition to legitimate users, there are illegal interceptors who try to steal secrets (also known as passive attacks) or tamper with messages (also known as active attacks) through various methods.

A cryptographic communication system can be shown in Figure 3.

Key: Divided into encryption key and decryption key.

Plain text: Information that is not directly encrypted and can directly represent the original meaning.

Ciphertext: After encryption processing, hide the original meaning of the information.

Encryption: The process of converting plain text to cipher text.

Decryption: The process of converting cipher text to plain text.

Cryptographic algorithm: The encryption method and decryption method adopted by the cryptographic system. With the development of mathematical cryptographic technology, the encryption method is generally called the encryption algorithm, and the decryption method is generally called the decryption algorithm.

Until modern times, cryptography almost exclusively referred to

In fact, secret letters were used in war before BC. Western "Father of History"

Password cracking is gradually generated and developed with the use of passwords. In 1412, the Persian Calle

Key authentication

Public Key Infrastructure (

Passive attack

Commitment schemes

Secure multiparty computations

Electronic voting

Certification

Digital signature

Cryptographic engineering

Crypto systems

1. Digital Signature:

This is a cryptographic method. According to the content of the EDI message and the private key sent, no one can generate the signature, so it is much more secure than a handwritten signature. The recipient uses the sender's public key for digital signature verification.

2. Digital Envelope:

This is a cryptographic method, using the recipient's public key to encrypt some confidential information. After receiving the message, the recipient decrypts it with his private key to read the secret.

As the main discipline of information security,

Military Science Overview, Shooting, Ballistics, Inner Ballistics, Outer Ballistics, Intermediate Ballistics, Terminal Ballistics, Missile Ballistics, Military Geography, Military Topography, Military Engineering, Military Meteorology, Military Medicine, Military Operations research, campaign science, cryptography, chemical warfare, etc.

The word Cryptology is derived from the Greek words "krypto's" and "logos". Literal translation means "hidden" and "message". Its use dates back to about four thousand years ago. In the year 2000, the Egyptians carved the sacrifice on the tombstone. Afterwards, people wrote secret messages on paper. In World War II, cryptography played a pivotal role. Many people think that the reason why the Allies can win this war is entirely due to the ciphertext digital computer invented during World War II to crack the German-Japanese password. In 1949, Shannon proposed the first paper to discuss the communication theory of cryptosystems. Modern cryptography can be said to have been in the past. Until 1975, Diffie and Hellman filed for open gold

The concept of key cryptosystems, the research direction of modern cryptography, has formally deviated from the secret of secret golden key cryptosystems, and has flourished. It has been nearly two decades. So far, there are two major types of cryptosystems. The first type is a symmetric key (Symmetric Key) cryptosystem, and the second type is an asymmetric key (Public Key) cryptosystem.

In 1965, the Department of Electrical Engineering at Stanford University-Merkel, Diffie, Hermann and others studied cryptography, but unfortunately nothing was found. In addition, Chernam, a secret agency of the British Communications and Electronic Security Group (CESG), found the recovery cipher, but because it belongs to a secret agency, it cannot be made public. It was not until 1977 that MIT graduate student Reeves discovered that Adman discovered a formula similar to that of Chelman. They set up RSA Security

Company (RSA is the prefix of their name), which is currently valued at $ 2.5 billion, has played a significant role in transferring credit cards. RSA has installed 500 million sets of products in IE, Netscape's small lock is RSA's product. The first discovery of mathematical write-off was not the United States, but? Was the first to be made public. Mathematical padlocks are easy to lock and difficult to restore, so they are widely used, which means that information coding is kept secret.

General examples of mathematical padlocks:

One-way formula for mathematical padlock: N = pxq <-example N (synthetic number) = multiplication of two prime numbers

11x17 = 187 = N

Restore the one-way formula: C = Me (mod N) * e is the number of times of M, because you can't type in Notepad *

M * 13 * (mod 187) = C * 13 is the number of times M

c = 165

x = 88 (password kiss)

88 * 13 * (mod 187) = 165 * 13 is the number of 88 *

modN = M

C * 1 / e * mod (p-1) (q-1) = 88

C = 165

p = 11

q = 17

answer: mod 187 = 88

There are generally two types of cryptography used:

Cryptography of symmetric key and public key (also called asymmetric key) .

As a simple example of symmetric key cryptography, suppose you receive a notification from a friend. You and your friend agree to encrypt and decrypt your message,

You will use the following algorithm: each letter will be moved up by three letters, for example A = C, B = D, and Y and Z will make a circle back to A and B,

This equation ("three letters up each letter") is the key that the sender uses to encrypt the message; the recipient uses the same key to decrypt it.

No one can read this message without a key. Because the same key is considered practical to encrypt and decrypt the message, this method is a symmetric key

Algorithm. This type of cryptography is known as secret key cryptography, because this key must be kept secretly between the sender and the recipient to protect the integrity of the data.

Asymmetric cryptography

Asymmetric or public key cryptography is different from symmetric cryptography in that its encryption key is only suitable for a single user.

The key is divided into two parts:

A private key, only owned by the user.

A public key, which can be issued and distributed publicly, and obtained whenever required.

Each key generates a function that is used to change the text. A private key generates a function that changes the text privately, and a public key generates a function to change the text publicly.

These functions are inversely related, for example, if one function is used to encrypt the message, the other function is used to decrypt the message. It does not matter whether the order of the function is changed.

The advantage of the public key system is that two users can communicate securely without exchanging secret keys. For example, suppose a sender needs to send a message to a recipient,

The confidentiality of the information is necessary. The sender is encrypted with the recipient's public key, and only the recipient's private key can decrypt the information.

Public key cryptography is well-suited for providing authenticated, complete and undeniable services, all of these services and digital signatures as we know them.

Basic principles of cryptography can be divided into two types: transposition and substitution.

The shift method is to change the order of the text in the message according to a certain rule. This method, when the number of text is large,

It can show its advantages. For example, "Hello World" can have 11708340914350080000 ways of arranging only 10 letters.

The other method, the substitution method , can also be divided into two types, one is single word substitution , one is letter substitution , and the principles of the two are the same.

It is to use the correspondence of the relative order of the text to change the original article. Taking English as an example, we can move the English letters back three positions, that is:

abcdefghijklmnopqrstu vwxyz

DEFGHIJKLMNOPQRSTUVWX YZABC

General example: Hello World How are you

khoor zruog krz duh brx

This sentence becomes difficult to recognize, and if the sender and recipient have an agreement, you can also delete the space between the text, anyway, when translated back,

The meaning of the sentence can be used to infer the timing of the hyphenation. For word replacement, each word is replaced with another corresponding word, so the original text is rewritten.

Into an encrypted file whose meaning cannot be discerned.

Of course, the shift method is not limited to only one. There are 25 different methods for English letters alone, regardless of case. Each cryptographic method can be regarded as an encryption method.

We call this a combination of algorithm and a key (KEY). The key is used to specify the calculation details of the encryption program. Take the shift method as an example,

The algorithm is to replace only the letters in the plaintext alphabet set with the letters in the cipher alphabet set, and the key is the cipher alphabet set defined by the sender and receiver.

The entire process of cryptography development, the process of identifying and finding new algorithms, and the process of protecting keys from being discovered by decrypters, keys are very important in cryptography, even if the algorithms are the same or too simple

Without the encryption key, it is still difficult for us to crack the encrypted file. With simple English letters, not just translation, but using letter-by-letter swap, regardless of capitalization,

There are 403291461126605635584000000 different kinds of keys that must be tested to get the original plaintext.

Quantum Cryptography (Jennewein et al., Quantum Cryptography with EntangledPhotons, Physical Review Letters, May 15, 2000, Vol 84, Iss 20, pp. 4729-4732)

For the first time, three independent research institutes have demonstrated the feasibility of using crypto-like features to construct passwords.

In this latest-and most secure-data encryption and decryption architecture (that is, quantum cryptography), researchers use a pair of entangled photons.

And even if the particles are far apart, they still have a close interaction.

Entanglement-based quantum cryptography has a unique, non-eavesdropping transmission characteristic. If an eavesdropper wants to steal information, it can be easily monitored.

In short, the entry process can create a complete, random sequence of 0s and 1s to provide users with data at both ends. If a hacker fetches data from it,

Then the message sequence will be changed, the user will find the eavesdropper and authorize to give up the eavesdropped material. This digital random sequence, or "golden key",

Then calculate with the data (such as mutual exclusion or gate XOR), that is, the encryption process, so that the data string forms a completely random sequence, this method is known as one-time pad cipher. Similarly,

The receiving end also relies on the golden key to perform the decryption process.

In the study, Los Alamos researchers simulated an eavesdropper to steal transmission data, were successfully detected, and authorized users to abandon the stolen data.

The research team in Australia has established a kilometer-long optical fiber to connect two completely independent transmissions and receiving stations to verify the entangled cryptographic theory.

They established the golden key and successfully transmitted the Venus image. At the same time, the team at the University of Geneva constructed more than several kilometers of optical fiber,

And use photon frequency to verify entangled cryptography theory.

In these experiments, although their transmission rate is slow, the angle-based cryptography theory is likely to surpass the non-entangled quantum cryptography theory in the future.

Not only the transmission rate, but also less extra photons needed to prevent data theft.

password strength

Password strength refers to the difficulty of a password being decoded by an unauthenticated user or computer. Password strength is usually described as "weak" or "strong". "Weak" and "strong" are relative. Different password systems have different requirements for password strength. Password cracking is related to the number of times the system allows customers to try different passwords, and whether they are familiar with the owner of the password. However, even strong passwords may be stolen, deciphered, or leaked. When setting a password, the user must set the password as complex as possible, the number of digits is longer, and frequently change this type of password. As high as possible.

A strong password should include: uppercase and lowercase letters, numbers, and symbols, and the length should not be too short, preferably no less than 10 digits. It does not contain information that can be easily guessed, such as birthdays and mobile phone numbers. In addition, it is recommended that you change your password regularly, and do not easily disclose your account number or password to others. The original code in 0 and 1 binary system can usually control the electronic components such as: 2 poles, 3 poles, etc.