md5
Synopsis
| cheia.load “md5” |
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| hash = md5.digest(data) |
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| context = md5.new() |
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| context:update(data) |
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| ... |
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| hash = context:digest() |
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| context:reset() |
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Description
This module provides a Lua interface to RSA's MD5 hash. This is a
cryptographic algorithm which calculates a ‘signature’ of a
data-stream, similar to a checksum. Unlike a checksum, MD5 is designed
to make it very difficult to manufacture a set of data to match a
given signature. This means that an MD5 digest can be used to verify
that data has not been modified, maliciously or otherwise.
Two interfaces are available:
- The md5.digest function provides a simple interface which returns
the digest of a supplied string.
- The md5.new function returns an object which will build a cumulative
digest over many calls to its update method.
Examples
Using the simple interface:
| print(md5.digest(“This is a test”)) |
» ce114e4501d2f4e2dcea3e17b546f339 |
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Or equivalently, using the context interface:
| context = md5.new() |
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| context:update(“This is ”) |
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| context:update(“a test”) |
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| print(context:digest()) |
» ce114e4501d2f4e2dcea3e17b546f339 |
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How the data is split does not alter the resulting digest, but its
order does:
| context = md5.new() |
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| context:update(“a test”) |
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| context:update(“This is ”) |
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| print(context:digest()) |
» 76344f576e34d222fe0a8dad3daecc8f |
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To compute the digest of a file in the same fashion as the md5sum utility, one might write:
| function md5sum(filename) |
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| local file = io.open(filename) |
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| if not file then return nil end |
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| -- Read the file in 4KB at a time |
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| local context = md5.new() |
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| local data = file:read(4096) |
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| while data do |
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| context:update(data) |
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| data = file:read(4096) |
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| end |
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| return context:digest() |
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| end |
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Reference
- md5.digest(data, [raw])
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Computes the digest of the given string. If raw is true, returns
the digest in binary form, otherwise returns a hex encoded version.
| Parameters: |
| data : string
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The data to be hashed.
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| raw : boolean
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If true, the digest will be returned in binary form.
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| Returns: |
| string
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The digest.
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- md5.new()
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Creates a new context for cumulatively calculating a digest.
| Returns: |
| userdata
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An MD5 context.
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The MD5 context
- context:update(data)
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Adds extra data to the digest. Can be called as many times as
required.
| Parameters: |
| data : string
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Data to be included in the digest.
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- context:digest([raw])
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Returns the digest of the concatentation of all the data added to
this context. If raw is true, returns the digest in binary form,
otherwise returns a hex encoded version.
Warning: Some extra data is added to the stream before the digest is
returned. This means that this method should be called once only,
once the stream is complete. It is not possible to obtain
intermediate results without affecting the digest value.
| Parameters: |
| raw : boolean
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If true, the digest will be returned in binary form.
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| Returns: |
| string
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The digest.
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- context:reset()
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Restores the context to its starting state, where no data has been
entered.
Issues
The digest method behaviour is unintuitive.
See also
RFC1321: The MD5 Message-Digest Algorithm, http://www.ietf.org/rfc/rfc1321.txt.
Revision history
Added in LuaCheia 5.0.
Credits
Based on the public domain C MD5 library by Colin Plumb.
Lua interface by Luiz Henrique de Figueiredo.
Modifications for LuaCheia by Thatcher Ulrich.
Documentation for LuaCheia by Jamie Webb.
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