Encryption methods such as RSA, only to protect the confidentiality of a message. In addition to the actual signature to protect the confidentiality you need another method, the author of a message proved to be documented. Usually this is done using cryptographic checksums, so-called hash functions. These are mathematical methods, from any plaintext according to a predetermined procedure a check (Compressed) generate. The function transforms a plaintext into a Compressed order that even the smallest change in the original text to a completely different check digit leads.

It belongs to the demands of this mathematical function that once generated from the Compressed not the original text can be reconstructed. Such a hash function is not reversible and is thus a one-way function. Unlike encryption, is a restoration of the initial text is not possible.

Moreover, the hash function as collision-free. Different messages with the same hash value should rarely occur. Thus, with a practically negligible uncertainty a specific hash value and the result of only one original plaintext.

The advantage of this procedure lies in the fact that instead of the entire article, just one short hash particularly needs to be protected.

For digital signature technology is the definition of a hash function. Available one-way hash functions are:

SHA/SHA-1 (Secure Hash Algorithm One)
SHA was developed by the NSA and a U.S. standard adopted. A slightly modified form, as the SHA-1 algorithm is now replaced. With SHA-1 hash is generated for the DSA (Digital Signature Algorithm), the DSS (Digital Signature Standard) is specified, are required. The hash has a length of 160 bit.

MD2, MD4, MD5 (Message Digest)
MD4 and MD5 hash functions are provided by R. Rivest (RSA Laboratories) and developed in conjunction with the standard PEM (Privacy Enhanced Mail) were presented. MD5 is a development of MD4. The algorithms generate a Message Digest (hash) of 128 bits in length.

RIPEMD-128, RIPEMD-160 (RIPE-Message Digest)
RIPEMD was funded under the EU project RIPE (RACE Integrity Primitives Evaluation, 1988-1992) was launched. (RIPE-Message Digest). Because cryptographic weaknesses of MD4 and MD5 RIPEMD was by Hans Dobbertin, Antoon Bosselaers and Bart Preneel developed. The hash value is either 128-bit (RIPEMD-128) or 160-bit (RIPEMD-160) long.

RSA Data Security is based on the weaknesses is that MD4 and MD5 hash for future functions should not be implemented. Generally offer hash functions with longer check higher security. Therefore, future SHA-1 or RIPEMD-160 can be used. RIPEMD-160 seems to be in Europe and SHA-1 in the U.S. as the de facto standard.

Only the combination of asymmetric encryption methods and hash values offers the possibility to have a human analogue to generate signature.

The means of cryptography experiment undertaken to obtain data on a variety of encryption methods to keep secret, is intended to safeguard the individual right to inviolability of privacy. Because it is precisely these data in the noise of the Internet to protect it when ordering, banking, during normal e-mail traffic or the general surfing through the Internet, via secure methods.

As always, show two sides - one of the experimental data must be protected and, consequently, attempts to break this protection. However, intelligence tests in the media slowly fruits.

Growing awareness of the citizens, but even more the massive pressure of the industry, a vital interest in secure communication has in the past year have led to a significant liberalization in this area led. The most widely used program for the secure encryption of e-mail, PGP (Pretty Good Privacy), was for years not be exported from the United States because it is military (!) Contained sensitive technology. Only on the detour, the printed source code from U.S. to Europe, again, new collections and to translate, it was possible, PGP and the rest of the world. This absurd state of affairs is now happily removed. Nevertheless, should continue to carefully make sure that state agencies are not re-create a backdoor to the population or the economy to eavesdrop. (sda / MHA)

Why these cryptographic methods are necessary, read in a separate contribution to the digital signature, the authorities soon, virtual courses via the Internet possible.