File Name: public and private key encryption .zip
A PDF can be protected in a number of ways. Most of the time it's sufficient to add a password - anyone who knows the PDF password can open it, and if the document author allowed it can print, copy text and so on. However if you want to allow only some users to print, this requires a different aproach. The simplest approach is to use Public Key Cryptography.
Encrypting and Decrypting PDF Documents
Public-key cryptography , or asymmetric cryptography , is a cryptographic system which uses pairs of keys : public keys which may be known to others , and private keys which may never be known by any except the owner. The generation of such key pairs depends on cryptographic algorithms which are based on mathematical problems termed one-way functions. Effective security requires keeping the private key private; the public key can be openly distributed without compromising security. In such a system, any person can encrypt a message using the intended receiver's public key , but that encrypted message can only be decrypted with the receiver's private key. This allows, for instance, a server program to generate a cryptographic key intended for a suitable symmetric-key cryptography , then to use a client's openly-shared public key to encrypt that newly-generated symmetric key.
A PDF document can be encrypted to protect its content from unauthorized access. The Standard Security handler allows you to define access permissions and up to two passwords: An user password, to open the document with respect to the defined access permissions and an owner password which will give you full access to the document. The Public-Key Security handler allows you to specify unique access permissions for different recipients. Only specified recipients will be able to open the encrypted PDF document. For encryption and decryption a pair of public and private key is used. For handlers of revision 3 or greater: Extract text and graphics in support of accessibility to users with disabilities or for other purposes. For handlers of revision 2: Copy or otherwise extract text and graphics from the document, including extracting text and graphics in support of accessibility to users with disabilities or for other purposes.
Modern cryptography exists at the intersection of the disciplines of mathematics , computer science , electrical engineering , communication science , and physics. Applications of cryptography include electronic commerce , chip-based payment cards , digital currencies , computer passwords , and military communications. Cryptography prior to the modern age was effectively synonymous with encryption , converting information from a readable state to unintelligible nonsense. The sender of an encrypted message shares the decoding technique only with intended recipients to preclude access from adversaries. The cryptography literature often uses the names Alice "A" for the sender, Bob "B" for the intended recipient, and Eve " eavesdropper " for the adversary.
The Public and Private key pair comprise of two uniquely related cryptographic keys basically long random numbers. Below is an example of a Public Key:. The Public Key is what its name suggests - Public. It is made available to everyone via a publicly accessible repository or directory. On the other hand, the Private Key must remain confidential to its respective owner. Because the key pair is mathematically related, whatever is encrypted with a Public Key may only be decrypted by its corresponding Private Key and vice versa. For example, if Bob wants to send sensitive data to Alice, and wants to be sure that only Alice may be able to read it, he will encrypt the data with Alice's Public Key.
called a Public key. The public key encrypt the message and sent to the recipient for decryption of the message. using the private key. Fig The encryption.
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Мы будем ждать. Джабба открыл рот. - Но, директор, ведь это… - Риск, - прервал его Фонтейн.
Сьюзан огляделась. Третий узел был пуст, свет шел от работающих мониторов. Их синеватое свечение придавало находящимся предметам какую-то призрачную расплывчатость. Она повернулась к Стратмору, оставшемуся за дверью.