Which Cryptography System Generates Encryption Keys

The generation and distribution of session keys are the most difficult in a cryptographic system, although many solutions have been proposed. SIHT uses an automatic method, which is transparent to users and eavesdroppers and based on a public key encryption algorithm, to avoid erroneous manipulations. 2010-9-16  Cryptography we are using AES algorithm to encrypt a message and a part of the message is hidden in DCT of an image; remaining part of the message is used to generate two secret keys which make this system highly secured. Keyword: Cryptography, Steganography, Stego- image, Threshold Value, DCT Coefficient 1.

In cryptography, a key is a piece of information (a parameter) that determines the functional output of a cryptographic algorithm. For encryption algorithms, a key specifies the transformation of plaintext into ciphertext, and vice versa for decryption algorithms. Keys also specify transformations in other cryptographic algorithms, such as digital signature schemes and message authentication codes.[1]

Need for secrecy[edit]

In designing security systems, it is wise to assume that the details of the cryptographic algorithm are already available to the attacker. This is known as Kerckhoffs' principle — 'only secrecy of the key provides security', or, reformulated as Shannon's maxim, 'the enemy knows the system'. The history of cryptography provides evidence that it can be difficult to keep the details of a widely used algorithm secret (see security through obscurity). A key is often easier to protect (it's typically a small piece of information) than an encryption algorithm, and easier to change if compromised. Thus, the security of an encryption system in most cases relies on some key being kept secret.[2]

Trying to keep keys secret is one of the most difficult problems in practical cryptography; see key management. An attacker who obtains the key (by, for example, theft, extortion, dumpster diving, assault, torture, or social engineering) can recover the original message from the encrypted data, and issue signatures.

Key scope[edit]

Keys are generated to be used with a given suite of algorithms, called a cryptosystem. Encryption algorithms which use the same key for both encryption and decryption are known as symmetric key algorithms. A newer class of 'public key' cryptographic algorithms was invented in the 1970s. These asymmetric key algorithms use a pair of keys—or keypair—a public key and a private one. Public keys are used for encryption or signature verification; private ones decrypt and sign. The design is such that finding out the private key is extremely difficult, even if the corresponding public key is known. As that design involves lengthy computations, a keypair is often used to exchange an on-the-fly symmetric key, which will only be used for the current session. RSA and DSA are two popular public-key cryptosystems; DSA keys can only be used for signing and verifying, not for encryption.

Ownership and revocation[edit]

Part of the security brought about by cryptography concerns confidence about who signed a given document, or who replies at the other side of a connection. Assuming that keys are not compromised, that question consists of determining the owner of the relevant public key. To be able to tell a key's owner, public keys are often enriched with attributes such as names, addresses, and similar identifiers. The packed collection of a public key and its attributes can be digitally signed by one or more supporters. In the PKI model, the resulting object is called a certificate and is signed by a certificate authority (CA). In the PGP model, it is still called a 'key', and is signed by various people who personally verified that the attributes match the subject.[3]

In both PKI and PGP models, compromised keys can be revoked. Revocation has the side effect of disrupting the relationship between a key's attributes and the subject, which may still be valid. In order to have a possibility to recover from such disruption, signers often use different keys for everyday tasks: Signing with an intermediate certificate (for PKI) or a subkey (for PGP) facilitates keeping the principal private key in an offline safe.

Deleting a key on purpose to make the data inaccessible is called crypto-shredding.

Key sizes[edit]

For the one-time pad system the key must be at least as long as the message. In encryption systems that use a cipher algorithm, messages can be much longer than the key. The key must, however, be long enough so that an attacker cannot try all possible combinations.

A key length of 80 bits is generally considered the minimum for strong security with symmetric encryption algorithms. 128-bit keys are commonly used and considered very strong. See the key size article for a more complete discussion.

The keys used in public key cryptography have some mathematical structure. For example, public keys used in the RSA system are the product of two prime numbers. Thus public key systems require longer key lengths than symmetric systems for an equivalent level of security. 3072 bits is the suggested key length for systems based on factoring and integer discrete logarithms which aim to have security equivalent to a 128 bit symmetric cipher. Elliptic curve cryptography may allow smaller-size keys for equivalent security, but these algorithms have only been known for a relatively short time and current estimates of the difficulty of searching for their keys may not survive. As early as 2004, a message encrypted using a 109-bit key elliptic curve algorithm had been broken by brute force.[4] The current rule of thumb is to use an ECC key twice as long as the symmetric key security level desired. Except for the random one-time pad, the security of these systems has not been proven mathematically as of 2018, so a theoretical breakthrough could make everything one has encrypted an open book (see P versus NP problem). This is another reason to err on the side of choosing longer keys.

Key choice[edit]

To prevent a key from being guessed, keys need to be generated truly randomly and contain sufficient entropy. The problem of how to safely generate truly random keys is difficult, and has been addressed in many ways by various cryptographic systems. There is a RFC on generating randomness (RFC 4086, Randomness Requirements for Security). Some operating systems include tools for 'collecting' entropy from the timing of unpredictable operations such as disk drive head movements. For the production of small amounts of keying material, ordinary dice provide a good source of high quality randomness.

Key vs password[edit]

For most computer security purposes and for most users, 'key' is not synonymous with 'password' (or 'passphrase'), although a password can in fact be used as a key. The primary practical difference between keys and passwords is that the latter are intended to be generated, read, remembered, and reproduced by a human user (though the user may delegate those tasks to password management software). A key, by contrast, is intended for use by the software that is implementing the cryptographic algorithm, and so human readability etc. is not required. In fact, most users will, in most cases, be unaware of even the existence of the keys being used on their behalf by the security components of their everyday software applications.

If a passwordis used as an encryption key, then in a well-designed crypto system it would not be used as such on its own. This is because passwords tend to be human-readable and, hence, may not be particularly strong. To compensate, a good crypto system will use the password-acting-as-key not to perform the primary encryption task itself, but rather to act as an input to a key derivation function (KDF). That KDF uses the password as a starting point from which it will then generate the actual secure encryption key itself. Various methods such as adding a salt and key stretching may be used in the generation.

See also[edit]

Cryptography Python

  • Cryptographic key types classification according to their usage
  • Diceware describes a method of generating fairly easy-to-remember, yet fairly secure, passphrases, using only dice and a pencil.
  • glossary of concepts related to keys

References[edit]

  1. ^'What is cryptography? - Definition from WhatIs.com'. SearchSecurity. Retrieved 2019-07-20.
  2. ^'Quantum Key Generation from ID Quantique'. ID Quantique. Retrieved 2019-07-20.
  3. ^Matthew Copeland; Joergen Grahn; David A. Wheeler (1999). Mike Ashley (ed.). 'The GNU Privacy Handbook'. GnuPG. Archived from the original on 12 April 2015. Retrieved 14 December 2013.
  4. ^Bidgoli, Hossein (2004). The Internet Encyclopedia. John Wiley. p. 567. ISBN0-471-22201-1 – via Google Books.
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定义

使用 RSA 算法加密数据。Encrypts data with the RSA algorithm.

重载

Encrypt(Byte[], Boolean)

使用 RSA 算法加密数据。Encrypts data with the RSA algorithm.

Encrypt(Byte[], RSAEncryptionPadding)

使用指定的填充,借助 RSA 算法对数据加密。Encrypts data with the RSA algorithm using the specified padding.

使用 RSA 算法加密数据。Encrypts data with the RSA algorithm.

参数

fOAEP
Boolean

如果为 true,则使用 OAEP 填充(仅可用于运行 Windows XP 及更高版本的计算机)执行直接 RSA 加密;否则,如果为 false,则使用 PKCS#1 v1.5 填充。true to perform direct RSA encryption using OAEP padding (only available on a computer running Windows XP or later); otherwise, false to use PKCS#1 v1.5 padding.

返回

已加密的数据。The encrypted data.

例外

无法获取加密服务提供程序 (CSP)。The cryptographic service provider (CSP) cannot be acquired.

Which Cryptography System Generates Encryption Keys Free

- 或 --or-rgb 参数的长度大于允许的最大长度。The length of the rgb parameter is greater than the maximum allowed length.

rgbnullrgb is null.

示例

下面的代码示例将 RSACryptoServiceProvider 对象初始化为公钥(由另一方发送)的值,使用 RijndaelManaged 算法生成会话密钥,然后使用 RSACryptoServiceProvider 对象对会话密钥进行加密。The following code example initializes an RSACryptoServiceProvider object to the value of a public key (sent by another party), generates a session key using the RijndaelManaged algorithm, and then encrypts the session key using the RSACryptoServiceProvider object.使用此方案时,可以将会话密钥发回到专用 RSA 密钥的所有者,并且双方都可以使用会话密钥来交换加密的数据。Using this scheme, the session key could be sent back to the owner of the private RSA key and the two parties could use the session key to exchange encrypted data.

注解

下表描述了不同版本的 Microsoft Windows 支持的填充,以及操作系统和填充的不同组合所允许的 rgb 的最大长度。The following table describes the padding supported by different versions of Microsoft Windows and the maximum length of rgb allowed by the different combinations of operating systems and padding.

填充PaddingRgb 参数的最大长度Maximum Length of rgb Parameter
OAEP 填充(PKCS # 1 v2)OAEP padding (PKCS#1 v2)模数大小-2-2 * hLen,其中 hLen 是哈希的大小。Modulus size -2 -2*hLen, where hLen is the size of the hash.
直接加密(PKCS # 1 1.5 版)Direct Encryption (PKCS#1 v1.5)模数大小-11。Modulus size - 11.(11个字节是可能的最小填充。)(11 bytes is the minimum padding possible.)

使用 Decrypt 解密此方法的结果。Use Decrypt to decrypt the results of this method.

另请参阅

使用指定的填充,借助 RSA 算法对数据加密。Encrypts data with the RSA algorithm using the specified padding.

参数

padding
RSAEncryptionPadding
Which cryptography system generates encryption keys free

Which Cryptography System Generates Encryption Keys Windows 10

填充。The padding.

返回

已加密的数据。The encrypted data.

例外

datanulldata is null.

- 或 --or-paddingnullpadding is null.

不支持该填充模式。The padding mode is not supported.

注解

padding 必须是 RSAEncryptionPadding.Pkcs1 或 RSAEncryptionPadding.OaepSHA1。padding must be either RSAEncryptionPadding.Pkcs1 or RSAEncryptionPadding.OaepSHA1.

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