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Definition: cryptography
The encrypting (scrambling) of data into a secret code. Cryptography is used to conceal messages transmitted over public networks such as the Internet (see HTTPS). It is used to encrypt storage drives and messages so that only authorized users have access (see BitLocker, ScramDisk and digital signature).
It's All Digital Today
Over the centuries, there have been many forms of cryptography, but today, all cryptographic processes are performed in a digital computer. See steganography.
From Plaintext to Ciphertext
A text message in its original form is called "plaintext." Using an encryption algorithm, the plaintext is turned into "ciphertext," which is indecipherable. To read the data, the ciphertext must be decrypted (unscrambled) and turned back into the original text (see plaintext).
Keys Are the Key
The encryption algorithm uses a "key," which is a binary number that is typically from 40 to 256 bits in length. The greater the number of bits in the key (cipher strength), the more possible key combinations and the longer it would take to break the code. The data are encrypted, or "locked," by combining the bits in the key mathematically with the data bits. At the receiving end, the key is used to "unlock" the code and restore the original data.
Secret vs. Public Key
Secret key cryptography and public key cryptography are the two primary encryption architectures.
Secret Keys - Symmetric System
The first method uses a secret key, such as the DES and AES algorithms. Both sender and receiver employ the same key to encrypt and decrypt. This is the fastest computation method, but getting the secret key to the recipient in the first place is a problem that is often handled by the next method. See DES and AES.
Public Keys - Asymmetric System
The second method uses a two-part key, such as RSA and El Gamal. Each recipient has a private key that is kept secret and a public key that is published for everyone. The sender looks up or is sent the recipient's public key and uses it to encrypt the message. The recipient uses the private key to decrypt the message and never publishes or transmits the private key to anyone. Thus, the private key is never in transit making it less susceptible to theft. See RSA.
Both Are Used Together
Secret key and public key systems are often used together, such as the AES secret key and the RSA public key. The secret key method provides the fastest decryption, and the public key method provides a convenient way to transmit the secret key. This is called a "digital envelope." For example, the PGP email encryption program uses one of several public key methods to send the secret key along with the message that has been encrypted with that secret key (see PGP).
Get Faster - Get Stronger
It has been said that any encryption code can be broken given enough time to compute all permutations. However, if it takes months to break a code, a war could be lost or a thief could have long absconded with stolen money. As computers get faster, encryption algorithms have to become stronger by using longer keys and more clever techniques (see quantum secure). See XOR, digital signature, digital certificate and chaff and winnow.
Secret Key vs. Public Key
Some Public History About Secret Methods
The following is reprinted with permission from RSA Security, Inc.
It's All Digital Today
Over the centuries, there have been many forms of cryptography, but today, all cryptographic processes are performed in a digital computer. See steganography.
From Plaintext to Ciphertext
A text message in its original form is called "plaintext." Using an encryption algorithm, the plaintext is turned into "ciphertext," which is indecipherable. To read the data, the ciphertext must be decrypted (unscrambled) and turned back into the original text (see plaintext).
Keys Are the Key
The encryption algorithm uses a "key," which is a binary number that is typically from 40 to 256 bits in length. The greater the number of bits in the key (cipher strength), the more possible key combinations and the longer it would take to break the code. The data are encrypted, or "locked," by combining the bits in the key mathematically with the data bits. At the receiving end, the key is used to "unlock" the code and restore the original data.
Secret key cryptography and public key cryptography are the two primary encryption architectures.
Secret Keys - Symmetric System
The first method uses a secret key, such as the DES and AES algorithms. Both sender and receiver employ the same key to encrypt and decrypt. This is the fastest computation method, but getting the secret key to the recipient in the first place is a problem that is often handled by the next method. See DES and AES.
Public Keys - Asymmetric System
The second method uses a two-part key, such as RSA and El Gamal. Each recipient has a private key that is kept secret and a public key that is published for everyone. The sender looks up or is sent the recipient's public key and uses it to encrypt the message. The recipient uses the private key to decrypt the message and never publishes or transmits the private key to anyone. Thus, the private key is never in transit making it less susceptible to theft. See RSA.
Both Are Used Together
Secret key and public key systems are often used together, such as the AES secret key and the RSA public key. The secret key method provides the fastest decryption, and the public key method provides a convenient way to transmit the secret key. This is called a "digital envelope." For example, the PGP email encryption program uses one of several public key methods to send the secret key along with the message that has been encrypted with that secret key (see PGP).
Get Faster - Get Stronger
It has been said that any encryption code can be broken given enough time to compute all permutations. However, if it takes months to break a code, a war could be lost or a thief could have long absconded with stolen money. As computers get faster, encryption algorithms have to become stronger by using longer keys and more clever techniques (see quantum secure). See XOR, digital signature, digital certificate and chaff and winnow.
The secret method uses the same key to encrypt and decrypt. The problem is transmitting the key to the recipient in order to use it. The public key method uses two keys: one kept private and never transmitted, while the other is made public. Very often, the public key method is used to safely send the secret key to the recipient so that the message can be encrypted using the faster secret key algorithm.
The following is reprinted with permission from RSA Security, Inc.