The modern One-Time Pad cipher is based on the Exclusive-OR, or XOR, operation. You have two streams of bits, the input and the key. Use them one bit at a time, the nth input bit with the nth key bit. So, the key stream must be as long as the input stream. In words: If the key bit is 0, the output bit is equal to the input bit. A one-time key is when the encryption scheme is set up such that only one message may be encrypted with a key. A many-time key is when multiple messages may be encrypted with a key. (A one-time-pad is a special case of a one-time key.) Example: CTR mode with a fixed IV is secure in the one-time key model, but insecure in the many-time key model. A one-time key is when the encryption scheme is set up such that only one message may be encrypted with a key. A many-time key is when multiple messages may be encrypted with a key. (A one-time-pad is a special case of a one-time key.) Example: CTR mode with a fixed IV is secure in the one-time key model, but insecure in the many-time key model. This automatically means that any construct that decreases the key space (like using a seed for a PRNG) severely weakens the one-time pad. Besides this a one-time pad (and the XOR based stream cipher) is very vulnerable to repeated-key attacks while there are other ciphers which are (more) secure against it.
In cryptography, a nonce is an arbitrary number that can be used just once in a cryptographic communication. It is similar in spirit to a nonce word, hence the name. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in replay attacks. They can also be useful as initialization vectors and in cryptographic hash functions.
A nonce is an arbitrary number used only once in a cryptographic communication, in the spirit of a nonce word. They are often random or pseudo-random numbers. Many nonces also include a timestamp to ensure exact timeliness, though this requires clock synchronization between organizations. The addition of a client nonce ('cnonce') helps to improve the security in some ways as implemented in digest access authentication. To ensure that a nonce is used only once, it should be time-variant (including a suitably fine-grained timestamp in its value), or generated with enough random bits to ensure a probabilistically insignificant chance of repeating a previously generated value. Some authors define pseudo-randomness (or unpredictability) as a requirement for a nonce.[1]
Authentication protocols may use nonces to ensure that old communications cannot be reused in replay attacks. For instance, nonces are used in HTTPdigest access authentication to calculate an MD5 digest of the password. The nonces are different each time the 401 authentication challenge response code is presented, thus making replay attacks virtually impossible. The scenario of ordering products over the Internet can provide an example of the usefulness of nonces in replay attacks. An attacker could take the encrypted information and—without needing to decrypt—could continue to send a particular order to the supplier, thereby ordering products over and over again under the same name and purchase information. The nonce is used to give 'originality' to a given message so that if the company receives any other orders from the same person with the same nonce, it will discard those as invalid orders.
A nonce may be used to ensure security for a stream cipher. Where the same key is used for more than one message and then a different nonce is used to ensure that the keystream is different for different messages encrypted with that key; often the message number is used.
Secret nonce values are used by the Lamport signature scheme as a signer-side secret which can be selectively revealed for comparison to public hashes for signature creation and verification.
Initialization vectors may be referred to as nonces, as they are typically random or pseudo-random.
Nonces are used in proof-of-work systems to vary the input to a cryptographic hash function so as to obtain a hash for a certain input that fulfills certain arbitrary conditions. In doing so, it becomes far more difficult to create a 'desirable' hash than to verify it, shifting the burden of work onto one side of a transaction or system. For example, proof of work, using hash functions, was considered as a means to combat email spam by forcing email senders to find a hash value for the email (which included a timestamp to prevent pre-computation of useful hashes for later use) that had an arbitrary number of leading zeroes, by hashing the same input with a large number of values until a 'desirable' hash was obtained.
Similarly, the bitcoinblockchain hashing algorithm can be tuned to an arbitrary difficulty by changing the required minimum/maximum value of the hash so that the number of bitcoins awarded for new blocks does not increase linearly with increased network computation power as new users join. This is likewise achieved by forcing bitcoin miners to add nonce values to the value being hashed to change the hash algorithm output. Because cryptographic hash algorithms cannot easily be predicted based on their inputs, this makes the act of blockchain hashing and the possibility of being awarded bitcoins something of a lottery, where the first 'miner' to find a nonce that delivers a desirable hash is awarded bitcoins.
Implements a cryptographic Random Number Generator (RNG) using the implementation provided by the cryptographic service provider (CSP). This class cannot be inherited.
The following code example shows how to create a random number with the RNGCryptoServiceProvider class.
Important
This type implements the IDisposable interface. When you have finished using the type, you should dispose of it either directly or indirectly. To dispose of the type directly, call its Dispose method in a try/catch block. To dispose of it indirectly, use a language construct such as using (in C#) or Using (in Visual Basic). For more information, see the 'Using an Object that Implements IDisposable' section in the IDisposable interface topic.
| RNGCryptoServiceProvider() | Initializes a new instance of the RNGCryptoServiceProvider class. |
| RNGCryptoServiceProvider(Byte[]) | Initializes a new instance of the RNGCryptoServiceProvider class. |
| RNGCryptoServiceProvider(CspParameters) | Initializes a new instance of the RNGCryptoServiceProvider class with the specified parameters. |
| RNGCryptoServiceProvider(String) | Initializes a new instance of the RNGCryptoServiceProvider class. |
| Dispose() | When overridden in a derived class, releases all resources used by the current instance of the RandomNumberGenerator class. (Inherited from RandomNumberGenerator) |
| Dispose(Boolean) | When overridden in a derived class, releases the unmanaged resources used by the RandomNumberGenerator and optionally releases the managed resources. (Inherited from RandomNumberGenerator) |
| Equals(Object) | Determines whether the specified object is equal to the current object. Windows pro 10 key generator. (Inherited from Object) |
| Finalize() | Frees resources used by the RNGCryptoServiceProvider class. |
| GetBytes(Byte[]) | Fills an array of bytes with a cryptographically strong sequence of random values. |
| GetBytes(Byte[], Int32, Int32) | Fills the specified byte array with a cryptographically strong random sequence of values starting at a specified index for a specified number of bytes. |
| GetBytes(Span<Byte>) | Fills a span with cryptographically strong random bytes. |
| GetHashCode() | Serves as the default hash function. (Inherited from Object) |
| GetNonZeroBytes(Byte[]) | Fills an array of bytes with a cryptographically strong sequence of random nonzero values. |
| GetNonZeroBytes(Span<Byte>) | Fills a byte span with a cryptographically strong random sequence of nonzero values. |
| GetType() | Gets the Type of the current instance. (Inherited from Object) |
| MemberwiseClone() | Creates a shallow copy of the current Object. (Inherited from Object) |
| ToString() | Returns a string that represents the current object. (Inherited from Object) |
This type is thread safe.