# Converters

# Measurement

## Inch

The inch (symbol: `in`

or `″`

) is a unit of length in the British imperial and the United States customary systems of measurement.
`1`

inch is `2.54`

centimeters.

## Foot

The foot (plural - feet, symbol: `ft`

or `'`

) is a unit of length in the British imperial and the United States customary systems of measurement.
`1`

foot is `30.48`

centimeters.

## Mile

The mile (symbol: `mi`

) is a unit of distance in the British imperial and the United States customary systems of measurement.
`1`

mile is `1.61`

kilometers.

## Pound

The pound or pound-mass (symbol: `lb`

) is a unit of mass in the British imperial and the United States customary systems of measurement.
`1`

pound is `0.45359237`

kilograms.

## Ounce

The ounce or ounce-mass (symbol: `oz`

) is a unit of mass in the British imperial and the United States customary systems of measurement.
`1`

ounce is `28.349523125`

grams (`1/16`

of pound).

## Gallon

The gallon (symbol: `US gal`

, `US dry gal`

, `imp gal`

) is a unit of volume in the British imperial and the United States customary systems of measurement.
`1`

US gallon is `3.785411784`

litres, `1`

US dry gallon is `4.40488377086`

litres, `1`

imperial gallon is `4.54609`

litres.

# Network

## CIDR

Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and IP routing.
Number after `/`

represents the number of network bits (unchanged and always `1`

) in the IP address.
The objective of CIDR it to improve the previous classful network addressing architecture
(3 classes - Class A: `/8`

, Class B: `/16`

, Class C: `/24`

).

# Encoding

## Base64

Base64 is an encoding algorithm that transform any characters (binary data) into an alphabet which consists `64`

symbols:
uppercase and lowercase Roman letters (`A–Z`

, `a–z`

), numerals (`0–9`

), `+`

and `/`

symbols.
The `=`

symbol is also used as a padding suffix (can be optional).

# Cryptographic

## MD5

The `MD5`

(Message Digest 5) is a cryptographic hash function which produces a `128-bit`

hash value.
It has been cryptographically broken and considered **insecure** (it should not be used).

## SHA-1

The `SHA-1`

(Secure Hash Algorithm 1) is a cryptographic hash function which produces a `160-bit`

hash value.
It has been cryptographically broken and considered **insecure** (it should not be used).

## SHA-2

The `SHA-2`

(Secure Hash Algorithm 2) is a set of cryptographic hash functions, it consists hash functions
which produce `224-bit`

, `256-bit`

, `384-bit`

or `512-bit`

hash values.

# Other

## htpasswd

The `htpasswd`

is used to store usernames and passwords for basic HTTP authentication (used in `Apache`

and `nginx`

). It supports different formats for password:

`bcrypt`

:`$2y$`

or`$2a$`

+ the result of the`crypt_blowfish`

algorithm.**Secure.**`MD5`

:`$apr1$`

+ the result of the`Apache-specific MD5 algorithm`

. Common but insecure.`SHA1`

:`{SHA}`

+ Base64-encoded SHA-1. Insecure.`CRYPT`

: Unix`crypt`

function with a randomly-generated 32-bit salt. Insecure.`PLAIN TEXT`

: Unencrypted. Insecure.