Nix Hash: Difference between revisions

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[https://en.wikipedia.org/wiki/Cryptographic_hash_function Cryptographic hashes] play an essential role in a lot of places in the Nix ecosystem. When using a hash somewhere, two criteria are essential to do so properly: the '''algorithm''' used and the '''encoding''' (and, to some extent, ''what'' is hashed).

Supported algorithms are <code>md5</code>, <code>sha1</code>, <code>sha256</code>, <code>sha512</code>. The first two are deprecated and should not be used anymore, but you may still stumble upon them in existing code.

Supported algorithms are <code>md5</code>, <code>sha1</code>, <code>sha256</code>, <code>sha512</code>, <code>BLAKE3</code>. The first two are deprecated and should not be used anymore, but you may still stumble upon them in existing code.

A hash – which is simply a sequence of bytes – is usually encoded in order to be representable as string. Common encodings are <code>base16</code> (commonly called "hex"), <code>base32</code> and <code>base64</code>. Note that the base32 is a [https://github.com/NixOS/nix/blob/~~master~~/src/libutil/hash.cc#~~L83~~-~~L107~~ '''custom one'''] that is not documented nor standardized in any way! If possible, use the provided hashing tools to convert hashes to it (see below). base32 is used by Nix in a lot of places because it is shorter than hex but can still safely be part of a file path (as it contains no slashes).

A hash – which is simply a sequence of bytes – is usually encoded in order to be representable as string. Common encodings are <code>base16</code> (commonly called "hex"), <code>base32</code> and <code>base64</code>. Note that the base32 is a [https://github.com/NixOS/nix/blob/c70e1433abb61012dffdcd4559ec2aa87672e15c/src/libutil/hash.cc#L91-L112 '''custom one'''] that is not documented nor standardized in any way! If possible, use the provided hashing tools to convert hashes to it (see below). base32 is used by Nix in a lot of places because it is shorter than hex but can still safely be part of a file path (as it contains no slashes).

== Usage ==

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When dealing with remote files, <code>nix-prefetch-url</code> offers a handy shortcut for downloading the file into the Nix store and printing out its hash. (<code>nix-prefetch-url --unpack</code> is its <code>fetchzip</code> equivalent.)

To get an SRI hash, which isn't supported by <code>nix-prefetch-url</code>, use <code>nix store prefetch-file https://...</code> instead.

== Libraries ==

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 [https://en.wikipedia.org/wiki/Cryptographic_hash_function Cryptographic hashes] play an essential role in a lot of places in the Nix ecosystem. When using a hash somewhere, two criteria are essential to do so properly: the '''algorithm''' used and the '''encoding''' (and, to some extent, ''what'' is hashed).
-Supported algorithms are <code>md5</code>, <code>sha1</code>, <code>sha256</code>, <code>sha512</code>. The first two are deprecated and should not be used anymore, but you may still stumble upon them in existing code.
+Supported algorithms are <code>md5</code>, <code>sha1</code>, <code>sha256</code>, <code>sha512</code>, <code>BLAKE3</code>. The first two are deprecated and should not be used anymore, but you may still stumble upon them in existing code.
-A hash – which is simply a sequence of bytes – is usually encoded in order to be representable as string. Common encodings are <code>base16</code> (commonly called "hex"), <code>base32</code> and <code>base64</code>. Note that the base32 is a [https://github.com/NixOS/nix/blob/master/src/libutil/hash.cc#L83-L107 '''custom one'''] that is not documented nor standardized in any way! If possible, use the provided hashing tools to convert hashes to it (see below). base32 is used by Nix in a lot of places because it is shorter than hex but can still safely be part of a file path (as it contains no slashes).
+A hash – which is simply a sequence of bytes – is usually encoded in order to be representable as string. Common encodings are <code>base16</code> (commonly called "hex"), <code>base32</code> and <code>base64</code>. Note that the base32 is a [https://github.com/NixOS/nix/blob/c70e1433abb61012dffdcd4559ec2aa87672e15c/src/libutil/hash.cc#L91-L112 '''custom one'''] that is not documented nor standardized in any way! If possible, use the provided hashing tools to convert hashes to it (see below). base32 is used by Nix in a lot of places because it is shorter than hex but can still safely be part of a file path (as it contains no slashes).
 == Usage ==
@@ Line 37: / Line 37: @@
 When dealing with remote files, <code>nix-prefetch-url</code> offers a handy shortcut for downloading the file into the Nix store and printing out its hash. (<code>nix-prefetch-url --unpack</code> is its <code>fetchzip</code> equivalent.)
+To get an SRI hash, which isn't supported by <code>nix-prefetch-url</code>, use <code>nix store prefetch-file https://...</code> instead.
 == Libraries ==