20-09-2014, 03:16 PM
[attachment=68254]cryptography
INTRODUCTION
Digital signature is a sort of Cryptography. Cryptography means keeping communications private. It is a practical art of converting messages or data into a different form, such that no one read them without having access to the ‘key’. The message may be converted using a ‘code’ (in which case each character or group of characters is substituted by an alternative one), or ‘cipher’ (in which case the message as a whole is converted, rather than individual characters). It deals with encryption, decryption and authentication.
There are two types of Cryptography-
1.Secret key or Symmetric Cryptography
2. Public key or Asymmetric Cryptography
In Symmetric Cryptography the sender and receiver of a message know and use the same secret key to encrypt the message, and the receiver uses same key to decrypt the message.
Asymmetric (or public key) Cryptography involves two related keys, one of which only the owner knows (the 'private key') and the other which anyone can know (the 'public key').
The advantages of Asymmetric Cryptography are that:
• Only one party needs to know the private key.
• The knowledge of the public key by a third party does not compromise security of message transmission.
The most important development from the work on public –key cryptography is Digital Signature.
What is digital signature
Basically, the idea behind digital signatures is the same as your handwritten signature. You use it to authenticate the fact that you promised something that you can't take back later. A digital signature doesn't involve signing something with a pen and paper then sending it over the Internet. But like a paper signature, it attaches the identity of the signer to a transaction. Having a digital certificate is like using your driver's license to verify your identity. You may have obtained your license from Maryland, for example, but your Maryland license lets you drive in Nevada and Florida. Similarly, your digital certificate proves your online identity to anybody who accepts it.
A digital signature can also be used to verify that information has not been altered after it was signed. A digital signature is an electronic signature to be used in all imaginable type of electronic transfer. Digital signature significantly differs from other electronic signatures in term of process and results. These differences make digital signature more serviceable for legal purposes.
DIGITAL SIGNATURE STANDARD :
The National Institute of Standards and Technology has published Federal Information processing standards Publications (FIPS PUBS), known as digital signature standard. The DSS makes use of the Secure Hash Algorithm (SHA) and present a new digital signature technique called the Digital Signature Algorithm (DSA) appropriate for applications requiring a digital rather than written signature. The DSA digital signature is a pair of large numbers represented in a computer as strings of binary digits. The digital signature is computed using a set of rules (i.e., the DSA) and a set of parameters such that the identity of the signatory and integrity of the data can be verified. The DSA provides the capability to generate and verify signatures. Signature generation makes use of a private key to generate a digital signature. Signature Verification makes use of a public key, which corresponds to, but is not the same as, the private key. Each user possesses a private and public key pair. Public keys are assumed signatures for stored as well as transmitted data. Anyone can verify the signature of a user by employing that user's public key. Signature generation can be performed only by the possessor of the user's private key.
A hash function is used in the signature generation process to obtain a condensed version of data, called a message digest (see Figure 1). The message digest is then input to the DSA to generate the digital signature. The digital signature is sent to the intended verifier along with the signed data (often called the message). The verifier of the message and signature verifies the signature by using the sender's public key. The same hash function must also be used in the verification process. The hash function is specified in a separate standard, the Secure Hash Standard (SHS), FIPS 180. Similar procedures may be used to generate and verify signatures for stored as well as transmitted data.
PURPOSE OF DIGITAL SIGNATURE
• Signer authentication :
If public and private keys are associated with an identified signer, the digital signature attributes the message to the signer. The digital signature cannot be forged, unless the signer loses control of the private key.
• Message authentication :
Digital signature identifies the signed message with far greater certainty and precision than paper signatures. Verification reveals any tempering since the comparison of hash result shows whether the message is the same as when signed.
• Non-repudiation :
Creating a digital signature requires the signer to use his private key. This alters the signer that he is consummating a transaction with legal consequences, decreasing the chances of litigation later on.
• Integrity :
Digital signature creation and verification processes provide a high level of assurance that the digital signature is that of the signer. Compared to tedious and labor intensive paper methods, such as checking signature cards, digital signatures yield a high degree of assurance without adding resources for processing.
INTRODUCTION
Digital signature is a sort of Cryptography. Cryptography means keeping communications private. It is a practical art of converting messages or data into a different form, such that no one read them without having access to the ‘key’. The message may be converted using a ‘code’ (in which case each character or group of characters is substituted by an alternative one), or ‘cipher’ (in which case the message as a whole is converted, rather than individual characters). It deals with encryption, decryption and authentication.
There are two types of Cryptography-
1.Secret key or Symmetric Cryptography
2. Public key or Asymmetric Cryptography
In Symmetric Cryptography the sender and receiver of a message know and use the same secret key to encrypt the message, and the receiver uses same key to decrypt the message.
Asymmetric (or public key) Cryptography involves two related keys, one of which only the owner knows (the 'private key') and the other which anyone can know (the 'public key').
The advantages of Asymmetric Cryptography are that:
• Only one party needs to know the private key.
• The knowledge of the public key by a third party does not compromise security of message transmission.
The most important development from the work on public –key cryptography is Digital Signature.
What is digital signature
Basically, the idea behind digital signatures is the same as your handwritten signature. You use it to authenticate the fact that you promised something that you can't take back later. A digital signature doesn't involve signing something with a pen and paper then sending it over the Internet. But like a paper signature, it attaches the identity of the signer to a transaction. Having a digital certificate is like using your driver's license to verify your identity. You may have obtained your license from Maryland, for example, but your Maryland license lets you drive in Nevada and Florida. Similarly, your digital certificate proves your online identity to anybody who accepts it.
A digital signature can also be used to verify that information has not been altered after it was signed. A digital signature is an electronic signature to be used in all imaginable type of electronic transfer. Digital signature significantly differs from other electronic signatures in term of process and results. These differences make digital signature more serviceable for legal purposes.
DIGITAL SIGNATURE STANDARD :
The National Institute of Standards and Technology has published Federal Information processing standards Publications (FIPS PUBS), known as digital signature standard. The DSS makes use of the Secure Hash Algorithm (SHA) and present a new digital signature technique called the Digital Signature Algorithm (DSA) appropriate for applications requiring a digital rather than written signature. The DSA digital signature is a pair of large numbers represented in a computer as strings of binary digits. The digital signature is computed using a set of rules (i.e., the DSA) and a set of parameters such that the identity of the signatory and integrity of the data can be verified. The DSA provides the capability to generate and verify signatures. Signature generation makes use of a private key to generate a digital signature. Signature Verification makes use of a public key, which corresponds to, but is not the same as, the private key. Each user possesses a private and public key pair. Public keys are assumed signatures for stored as well as transmitted data. Anyone can verify the signature of a user by employing that user's public key. Signature generation can be performed only by the possessor of the user's private key.
A hash function is used in the signature generation process to obtain a condensed version of data, called a message digest (see Figure 1). The message digest is then input to the DSA to generate the digital signature. The digital signature is sent to the intended verifier along with the signed data (often called the message). The verifier of the message and signature verifies the signature by using the sender's public key. The same hash function must also be used in the verification process. The hash function is specified in a separate standard, the Secure Hash Standard (SHS), FIPS 180. Similar procedures may be used to generate and verify signatures for stored as well as transmitted data.
PURPOSE OF DIGITAL SIGNATURE
• Signer authentication :
If public and private keys are associated with an identified signer, the digital signature attributes the message to the signer. The digital signature cannot be forged, unless the signer loses control of the private key.
• Message authentication :
Digital signature identifies the signed message with far greater certainty and precision than paper signatures. Verification reveals any tempering since the comparison of hash result shows whether the message is the same as when signed.
• Non-repudiation :
Creating a digital signature requires the signer to use his private key. This alters the signer that he is consummating a transaction with legal consequences, decreasing the chances of litigation later on.
• Integrity :
Digital signature creation and verification processes provide a high level of assurance that the digital signature is that of the signer. Compared to tedious and labor intensive paper methods, such as checking signature cards, digital signatures yield a high degree of assurance without adding resources for processing.