Decodes a URL safe base 64 string to binary

Encodes a binary as a URL safe base 64 string

Example

iex> Apoc.encode(<<16, 32, 64>>)
"ECBA"

Encoding Scheme

Base 64 is similar to hex encoding but now instead of using 4-bit nibbles it uses groups of 6 bits (64 possible values) and then assigns each to a character as defined here https://hexdocs.pm/elixir/Base.html#module-base-64-url-and-filename-safe-alphabet.

The algorithm is a little more complex now as we have to worry about padding to the nearest mulitple of 6 bytes. However, a simple example can be demonstrated with 3 bytes which is 24 bits and already a mulitple of 6.

Take the binary <<10, 10, 10>>, we can break it into 6-bit components:

iex> <<a::6, b::6, c::6, d::6>> = <<10, 10, 10>>
...> [a, b, c, d]
[2, 32, 40, 10]

Now mapping each value to the safe alphabet we get:

iex> Apoc.encode(<<10, 10, 10>>)
"CgoK"

Hash a message with the default hashing scheme and encode it with Apoc.encode/1.

See Apoc.Hash for other hashing schemes and encoding options

Encodes a binary in hex format.

Hex strings represent a binary by splitting each byte into two parts of 4-bits (called a “nibble”).

Each nibble has 16 possible values, 0 through to 15. Values 0 to 9 stay as they are while values 10 to 15 are mapped to the letters a through to h.

Example

iex> Apoc.hex(<<27, 90, 33, 46>>)
"1b5a212e"

Encoding Scheme

The binary <<184>> splits into the nibbles x and y:

iex> <<x::4, y::4>> = <<184>>
...> [x, y]
[11, 8]

Now 11 maps to the character “b” while 8 stays the same so the hex encoding of the byte <<184>> is “b8”.

iex> Apoc.hex(<<184>>)
"b8"

Note that hex strings are exactly twice as long (in bytes) as the original binary.

See also Base.encode16/2

Simple wrapper to :crypto.strong_rand_bytes/1. Returns a secure binary of num random bytes

Compares to bitlists for equality in constant time to avoid timing attacks.

See https://codahale.com/a-lesson-in-timing-attacks/ and Plug.Crypto.