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=head1 NAME |
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Crypt::Ed25519 - bare-bones Ed25519 public key signing/verification system |
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=head1 SYNOPSIS |
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use Crypt::Ed25519; # no symbols exported |
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|
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############################################ |
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# Ed25519 API - public/private keypair |
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|
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# generate a public/private key pair once |
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($pubkey, $privkey) = Crypt::Ed25519::generate_keypair; |
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|
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# sign a message |
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$signature = Crypt::Ed25519::sign $message, $pubkey, $privkey; |
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|
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# verify message |
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$valid = Crypt::Ed25519::verify $message, $pubkey, $signature; |
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|
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# verify, but croak on failure |
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Crypt::Ed25519::verify_croak $message, $pubkey, $signature; |
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|
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############################################ |
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# EdDSA API - secret key and derived public key |
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|
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# generate a secret key |
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$secret = Crypt::EdDSA::eddsa_secret_key; |
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|
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# derive public key as needed |
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$pubkey = Crypt::EdDSA::eddsa_public_key $secret; |
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|
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# sign a message |
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$signature = Crypt::Ed25519::eddsa_sign $message, $pubkey, $secret; |
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|
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# verify message |
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$valid = Crypt::Ed25519::eddsa_verify $message, $pubkey, $signature; |
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|
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# verify, but croak on failure |
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Crypt::Ed25519:eddsa_verify_croak $message, $pubkey, $signature; |
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|
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############################################ |
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# Curve25519 key exchange |
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|
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# side A: |
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($pubkey_a, $privkey_a) = Crypt::Ed25519::generate_keypair; |
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# send $pubkey to side B |
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|
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# side B: |
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($pubkey_b, $privkey_b) = Crypt::Ed25519::generate_keypair; |
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# send $pubkey to side A |
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|
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# side A then calculates their shared secret: |
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$shared_secret = Crypt::Ed25519::key_exchange $pubkey_b, $privkey_a; |
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|
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# and side B does this: |
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$shared_secret = Crypt::Ed25519::key_exchange $pubkey_a, $privkey_b; |
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|
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# the generated $shared_secret will be the same - you cna now |
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# hash it with hkdf or something else to generate symmetric private keys |
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|
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=head1 DESCRIPTION |
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|
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This module implements Ed25519 public key generation, message signing and |
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verification. It is a pretty bare-bones implementation that implements |
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the standard Ed25519 variant with SHA512 hash, as well as a slower API |
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compatible with the upcoming EdDSA RFC. |
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|
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The security target for Ed25519 is to be equivalent to 3000 bit RSA or |
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AES-128. |
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|
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The advantages of Ed25519 over most other signing algorithms are: |
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small public/private key and signature sizes (<= 64 octets), good key |
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generation, signing and verification performance, no reliance on random |
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number generators for signing and by-design immunity against branch or |
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memory access pattern side-channel attacks. |
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|
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More detailed praise and other info can be found at |
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L<http://ed25519.cr.yp.to/index.html>. |
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|
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=head1 CRYPTOGRAPHY IS HARD |
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A word of caution: don't use this module unless you really know what you |
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are doing - even if this module were completely error-free, that still |
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doesn't mean that every way of using it is correct. When in doubt, it's |
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best not to design your own cryptographic protocol. |
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|
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=head1 CONVENTIONS |
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|
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Public/private/secret keys, messages and signatures are all opaque and |
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architecture-independent octet strings, and, except for the message, have |
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fixed lengths. |
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|
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=cut |
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|
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package Crypt::Ed25519; |
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|
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BEGIN { |
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$VERSION = 1.05; |
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|
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require XSLoader; |
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XSLoader::load Crypt::Ed25519::, $VERSION; |
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} |
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|
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=head1 Ed25519 API |
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=over 4 |
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|
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=item ($public_key, $private_key) = Crypt::Ed25519::generate_keypair |
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Creates and returns a new random public and private key pair. The public |
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key is always 32 octets, the private key is always 64 octets long. |
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=item ($public_key, $private_key) = Crypt::Ed25519::generate_keypair $secret_key |
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|
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Instead of generating a random keypair, generate them from the given |
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C<$secret_key> (e.g. as returned by C<Crypt::Ed25519::eddsa_secret_key>. |
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The derivation is deterministic, i.e. a specific C<$secret_key> will |
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always result in the same keypair. |
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A secret key is simply a random bit string, so if you have a good source |
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of key material, you can simply generate 32 octets from it and use this as |
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your secret key. |
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=item $signature = Crypt::Ed25519::sign $message, $public_key, $private_key |
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Generates a signature for the given message using the public and private |
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keys. The signature is always 64 octets long and deterministic, i.e. it is |
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always the same for a specific combination of C<$message>, C<$public_key> |
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and C<$private_key>, i.e. no external source of randomness is required for |
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signing. |
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=item $valid = Crypt::Ed25519::verify $message, $public_key, $signature |
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Checks whether the C<$signature> is valid for the C<$message> and C<$public_ke>. |
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=item Crypt::Ed25519::verify_croak $message, $public_key, $signature |
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Same as C<Crypt::Ed25519::verify>, but instead of returning a boolean, |
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simply croaks with an error message when the signature isn't valid, so you |
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don't have to think about what the return value really means. |
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|
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=back |
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=head1 EdDSA compatible API |
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|
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The upcoming EdDSA draft RFC uses a slightly different (and slower) |
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API for Ed25519. This API is provided by the following functions: |
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|
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=over 4 |
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|
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=item $secret_key = Crypt::Ed25519::eddsa_secret_key |
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Creates and returns a new secret key, which is always 32 octets |
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long. The secret key can be used to generate the public key via |
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C<Crypt::Ed25519::eddsa_public_key> and is not the same as the private key |
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used in the Ed25519 API. |
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|
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A secret key is simply a random bit string, so if you have a good source |
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of key material, you can simply generate 32 octets from it and use this as |
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your secret key. |
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|
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=item $public_key = Crypt::Ed25519::eddsa_public_key $secret_key |
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Takes a secret key generated by C<Crypt::Ed25519::eddsa_secret_key> |
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and returns the corresponding C<$public_key>. The derivation is |
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deterministic, i.e. the C<$public_key> generated for a specific |
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C<$secret_key> is always the same. |
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This public key corresponds to the public key in the Ed25519 API above. |
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=item $signature = Crypt::Ed25519::eddsa_sign $message, $public_key, $secret_key |
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Generates a signature for the given message using the public and secret |
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keys. Apart from specifying the C<$secret_key>, this function is identical |
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to C<Crypt::Ed25519::sign>, so everything said about it is true for this |
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function as well. |
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|
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Internally, C<Crypt::Ed25519::eddsa_sign> derives the corresponding |
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private key first and then calls C<Crypt::Ed25519::sign>, so it is always |
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slower. |
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|
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=item $valid = Crypt::Ed25519::eddsa_verify $message, $public_key, $signature |
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=item Crypt::Ed25519::eddsa_verify_croak $message, $public_key, $signature |
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Really the same as C<Crypt::Ed25519::verify> and |
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C<Crypt::Ed25519::verify_croak>, i.e. the functions without the C<eddsa_> |
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prefix. These aliases are provided so it's clear that you are using EdDSA |
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and not Ed25519 API. |
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|
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=back |
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=head1 CONVERTING BETWEEN Ed25519 and EdDSA |
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|
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The Ed25519 and EdDSA compatible APIs handle keys slightly |
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differently: The Ed25519 API gives you a public/private key pair, while |
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EdDSA takes a secret and generates a public key from it. |
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You can convert an EdDSA secret to an Ed25519 private/public key pair |
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using C<Crypt::Ed25519::generate_keypair>: |
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($public_key, $private_key) = Crypt::Ed25519::generate_keypair $secret |
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As such, the EdDSA-style API allows you to store only the secret key and |
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derive the public key as needed. On the other hand, signing using the |
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private key is faster than using the secret key, so converting the secret |
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key to a public/private key pair allows you to sign a small message, or |
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many messages, faster. |
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|
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=head1 Curve25519 Key Exchange |
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As an extension to Ed25519, this module implements a key exchange similar |
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to Curve25519, which should be compatible to other implementations of |
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Curv25519, depending on how the resulting shared secret is hashed. |
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To do this, both sides generate a keypair and send their public key to the |
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other side. Then both sides can generate the same shared secret using this |
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function: |
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|
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=over |
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=item $shared_secret = Crypt::Ed25519::key_exchange $other_public_key, $own_private_key |
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Return the 32 octet shared secret generated from the given public and |
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private key. |
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The resulting C<$shared_key> should be hashed before use (for example, by |
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using it in a KDF such as HKDF). |
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See SYNOPSIS for an actual example. |
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|
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=back |
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|
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=head1 SUPPORT FOR THE PERL MULTICORE SPECIFICATION |
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|
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This module supports the perl multicore specification |
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(L<http://perlmulticore.schmorp.de/>) for all operations, although it |
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makes most sense to use it when signing or verifying longer messages. |
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=head1 IMPLEMENTATION |
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|
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This module currently uses "Nightcracker's Ed25519" implementation, which |
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is unmodified except for some portability fixes and static delcarations, |
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but the interface is kept implementation-agnostic to allow usage of other |
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implementations in the future. |
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|
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=head1 AUTHOR |
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|
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Marc Lehmann <schmorp@schmorp.de> |
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http://software.schmorp.de/pkg/Crypt-Ed25519.html |
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=cut |
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1 |
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