Private key

The blowdown valves on the boilers were operated by a special key, which had a lug on it so that it could not be removed when the valve was open. It was therefore impossible, in theory, for two blowdown valves to be open at the same time. However, the boiler fitter kept and jealously guarded a private key w ithout a lug and had used this one to open the blowdown valve on the boiler that was under repair. He forgot to tell the process foreman what he had done or to close the valve. The presence of this key would appear to have been of little moment as long as the correct procedure of complete isolation was maintained, but as soon as it was departed from, the additional key became a menace, which eventually enabled the present tragedy to occur, the accident report said. 

Encrypt Hash Key Using Personal Private Key Witness Signature ... 

In order to sign a record, the record and the private key form the inputs to a hashing process. 

If the digital signature was computed with a private key other than the one corresponding to the public key used for verification, then the verification will fail... 

In digital signatures, the private key signs, and the public key verily the authenticity of signatures. For confidentiality, the public key encrypts messages, and the private key decrypts messages. 

In 1976, Whitfield Diffie developed public-key encryption as an alternative to private-key encryption. Public-key encryption is based on two halves of the same key that are generated with special software at the same time. The key pair are mathematically related so that the private key cannot be determined from the public key. Only one of the two halves of the key pair is required to encrypt a message, with the other half being used for decryption. In public key cryptography, one half of the key pair (the private key) is assigned to an individual, and is closely guarded and securely stored on the user s local disk in either an encrypted format or as part of a token that interfaces with the computer. The other half of the key is published in a public directory where all users can access it and this therefore referred to as the public key. 

Public-key cryptography, when properly implemented and used, enables people to communicate in secrecy, and to sign documents, with almost absolute security and without ever having to exchange a private key. 

One well-known product based on PKCS is the PKI. PKI is a combination of software, encryption technologies, server platforms, workstations, policies, and services used for administering certificates and public-private key pairs. 

In a traditional PKI architecture, a CA is a trusted party that vouches for the authenticity for the entity in question. The CA notarizes public keys by digitally signing the certificates using the CA s private key, which is linked to the entities5 concerned. 

Watermark extraction in the Zhao-Koch algorithm is performed by analyzing the relationships between three pseudo-randomlv chosen coefficients in each DOT block, as described in the previous section. The coefficient locations are generated as a function of the watermark owner s private key, and are chosen from a set of eight possible locations in each block. 

Cryptographic algorithms can be unbreakable in theory, but they must be implemented in practice. The implementation may not be flaws free, and the private key of a signatory can be compromised. Cryptographic tokens, where... 

The key distribution problem can be avoided by the Public Key System (PKS) which was invented in the 1970s.The idea is based on each secret communication participant having two keys. One public key for encryption and the second private key for decryption. If Alice wants to send a confidential message to Bob she encryptsher plain message using Bob s public key. Bob decrypts the cryptotext using his private key which is complementary to his public key. 

Additionally, all the content to which ownership has been transferred to a person, for example by purchase, also becomes personal content. For example, a digital certificate issued by a Certification Authority, and purchased by the person, becomes personal content as it contains a public key that is bound to the person s private key. 

Digital certificates ensure private and secure submission of electronic documents. The digital certificate binds together the owner s name and a pair of electronic keys (a public key and a private key) that can be used to encrypt and sign documents. 

Asymmetric encryption is also called public key encryption. Two keys are required a private key and a public key. Usually the sender encrypts the data with the public key and the receiver decrypts the data with a private key but it can also be the other way arormd. Public keys are frequently located on the Internet. Private keys are located in a secure area of the owner s computer. 

Such a scheme is intended to be used as follows Everybody who may want to sign messages generates such a key pair. She keeps the signing key secret and publishes the test key. (For simplicity, signers will always be assumed to be female and recipients male, corresponding to the names used in the figures.) Alternatively, the two keys are therefore called secret key (or private key) and public key, respectively. 

This can be done by using so-called mix servers [58], [57]. A mix server makes tracing of data packets nearly impossible. It receives a packet (which has to be encrypted), re-codes it, and forwards it with some delay. This delay causes several packets received by the mix server to be permuted in their order in the sending process. The re-coding is done with an asymmetric encryption method. The sender encrypts the packet with the public key of the mix server, the mix server decrypts it with the corresponding private key and forwards it. It is also possible to create a chain of mix servers for increased security. Due to the delay caused for decrypting and also for forwarding the packets in a different order, this techniques is unsuited for sjmchronous communication. 

In contrast with secret key cryptography, public key cryptography is based on separate encryption and decryption keys, where one of them can be published. Anyone can use that public key to encrypt a message that only the owner of the private key... 

In asymmetric cryptography, the locks are referred to as public keys, and the keys for the locks are referred to as private keys. 

The locked record management system completely hides the content of electronic records from others, including system/data administrators, by storing the electronic records encrypted with the owner s public key and again with the custodian s private key so that only the owner of the electronic records can decrypt them in collaboration with the custodian. The sealed record management system completely hides the existence of such electronic records, as well as its content, from others, including system/data administrators, by storing the metadata (i.e., the information about the electronic record) encrypted with the owner s public key so that only the owner of the electronic records may know about and get the information about the existence of the electronic records. 

This asymmetric cryptography approach also protects the existence of the electronic record by storing the record identifier in an encrypted format. This is achieved by encrypting the electronic record identifier with the record owner s private key. Therefore only the ones who have access to the public key of the record owner can access the record identifier. 

Sender encrypts a document with a personal private key code, then encrypts it again with the receiver s public key. 

One particular problem with state-of-the-art watermarking schemes is that they are symmetric. The keys necessary for watermark embedding and detection are identical. Thus, the watermark detector knows all critical parameter of the watermarking scheme that also allow efficient removal of the embedded watermark. We will discuss such methods in more detail in Section 3. Using watermark technology for copy protection, the watermark detector needs to be implemented in many cheap consumer devices all over the world. A symmetric watermarking scheme presents a security risk, since the detector has to know the required private key. However, cheap tamper-proof devices are... 

First, we will explain our notation and describe a general point of view on watermarking schemes in Section 2. For a better understanding of the differences between symmetric and asymmetric schemes, both methods are described. In Section 3, we will discuss two symmetric watermarking schemes and possible attacks if the private key can be accessed by an attacker. Several proposals of asymmetric watermarking schemes are discussed in Section 4. Finally, an assessment of the state-of-the-art is given, and future research directions are proposed. 

Fig. 1 depicts a general blind symmetric watermarking scheme. The term blind indicates that the host signal x is not known at the watermark detector. The watermark information b is embedded into the host signal x dependent on a private key. All modifications introdnced by the embedding process are denoted by the watermark signal w, so that the public signal s can be expressed as s = x -I- w. The distortion introduced... 

Finally, the detector computes an estimate h of the transmitted watermark information 6, depending on the private key and the received signal r. The probability Pr(fo 7 h) of false detection should be as small as possible. 

A random signal z is defined. For instance, the samples z [i] can be drawn independently and equiprobably from the binary alphabet -1, -I-1. z serves as the private key of the watermarking scheme. Watermark embedding is implemented by simple addition of the watermark signal w = baz. The scale factor a determines the power of the watermark signal and must be chosen such that the watermark is imperceptible, but sufficient reliably detectable. The factor b e B depends on the watermark information to be transmitted. For instance, tmipolar transmission is obtained for B = 0,1, and for bipolar transmission B = -l, + 1. ... 

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