

DMZ host
Some home routers refer to a DMZ host. A home router DMZ host is a single address (e.g., IP address) on the internal network that has all traffic sent to it which is not otherwise forwarded to other LAN hosts. By definition this is not a true DMZ (demilitarized zone), since it alone does not separate the host from the internal network. That is, the DMZ host is able to connect to hosts on the internal network, whereas hosts within a real DMZ are prevented from connecting with the internal network by a firewall that separates them, unless the firewall permits the connection. A firewall may allow this if a host on the internal network first requests a connection to the host within the DMZ. The DMZ host provides none of the security advantages that a subnet provides and is often used as an easy method of forwarding all ports to another firewall / NAT device. This tactic (establishing a DMZ host) is also used with systems which do not interact properly with normal firewalling rules or NAT. This can be because no forwarding rule can be formulated ahead of time (varying TCP or UDP port numbers for example, as opposed to a fixed number or fixed range). This is also used for network protocols for which the router has no programming to handle (6in4 or GRE tunnels are prototypical examples). What isHash-based message authentication code
![In cryptography, a keyed-hash message authentication code (HMAC) is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret cryptographic key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authentication of a message. Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key. An iterative hash function breaks up a message into blocks of a fixed size and iterates over them with a compression function. For example, MD5 and SHA-1 operate on 512-bit blocks. The size of the output of HMAC is the same as that of the underlying hash function (128 or 160 bits in the case of MD5 or SHA-1, respectively), although it can be truncated if desired. The definition and analysis of the HMAC construction was first published in 1996 by Mihir Bellare, Ran Canetti, and Hugo Krawczyk,[1] who also wrote RFC 2104. This paper also defined a variant called NMAC that is rarely, if ever, used. FIPS PUB 198 generalizes and standardizes the use of HMACs. HMAC-SHA1 and HMAC-MD5 are used within the IPsec and TLS protocols.](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/SHAhmac.svg/400px-SHAhmac.svg.png)
In cryptography, a keyed-hash message authentication code (HMAC) is a specific construction for calculating a message authentication code (MAC) involving a cryptographic hash function in combination with a secret cryptographic key. As with any MAC, it may be used to simultaneously verify both the data integrity and the authentication of a message. Any cryptographic hash function, such as MD5 or SHA-1, may be used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA1 accordingly. The cryptographic strength of the HMAC depends upon the cryptographic strength of the underlying hash function, the size of its hash output, and on the size and quality of the key. An iterative hash function breaks up a message into blocks of a fixed size and iterates over them with a compression function. For example, MD5 and SHA-1 operate on 512-bit blocks. The size of the output of HMAC is the same as that of the underlying hash function (128 or 160 bits in the case of MD5 or SHA-1, respectively), although it can be truncated if desired. The definition and analysis of the HMAC construction was first published in 1996 by Mihir Bellare, Ran Canetti, and Hugo Krawczyk,[1] who also wrote RFC 2104. This paper also defined a variant called NMAC that is rarely, if ever, used. FIPS PUB 198 generalizes and standardizes the use of HMACs. HMAC-SHA1 and HMAC-MD5 are used within the IPsec and TLS protocols.
- Take the full URL of the request URL you specify for your phone number or app, from the protocol (https…) through the end of the query string (everything after the ?).
- If the request is a POST, sort all of the POST parameters alphabetically (using Unix-style case-sensitive sorting order).
- Iterate through the sorted list of POST parameters, and append the variable name and value (with no delimiters) to the end of the URL string.
- Sign the resulting string with HMAC-SHA1 using your AuthToken as the key (remember, your AuthToken’s case matters!).
- Base64 encode the resulting hash value.
- Compare your hash to ours, submitted in the X-Twilio-Signature header. If they match, then you’re good to go.