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NAME |
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Crypt::Ed25519 - bare-bones Ed25519 public key signing/verification |
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system |
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|
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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, $signature; |
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|
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############################################ |
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# Key exchange |
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|
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# side A: |
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($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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DESCRIPTION |
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This module implements Ed25519 public key generation, message signing |
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and verification. It is a pretty bare-bones implementation that |
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implements the standard Ed25519 variant with SHA512 hash, as well as a |
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slower API 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: small |
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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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<http://ed25519.cr.yp.to/index.html>. |
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|
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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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CONVENTIONS |
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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, |
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have fixed lengths. |
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|
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Ed25519 API |
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($public_key, $private_key) = Crypt::Ed25519::generate_keypair |
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Creates and returns a new random public and private key pair. The |
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public key is always 32 octets, the private key is always 64 octets |
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long. |
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|
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($public_key, $private_key) = Crypt::Ed25519::generate_keypair |
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$secret_key |
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Instead of generating a random keypair, generate them from the given |
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$secret_key (e.g. as returned by "Crypt::Ed25519::eddsa_secret_key". |
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The derivation is deterministic, i.e. a specific $secret_key will |
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always result in the same keypair. |
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|
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A secret key is simply a random bit string, so if you have a good |
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source of key material, you can simply generate 32 octets from it |
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and use this as your secret key. |
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|
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$signature = Crypt::Ed25519::sign $message, $public_key, $private_key |
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Generates a signature for the given message using the public and |
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private keys. The signature is always 64 octets long and |
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deterministic, i.e. it is always the same for a specific combination |
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of $message, $public_key and $private_key, i.e. no external source |
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of randomness is required for signing. |
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|
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$valid = Crypt::Ed25519::verify $message, $public_key, $signature |
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Checks whether the $signature is valid for the $message and |
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$public_ke. |
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|
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Crypt::Ed25519::verify_croak $message, $public_key, $signature |
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Same as "Crypt::Ed25519::verify", but instead of returning a |
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boolean, simply croaks with an error message when the signature |
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isn't valid, so you don't have to think about what the return value |
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really means. |
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|
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EdDSA compatible API |
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The upcoming EdDSA draft RFC uses a slightly different (and slower) API |
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for Ed25519. This API is provided by the following functions: |
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|
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$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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"Crypt::Ed25519::eddsa_public_key" and is not the same as the |
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private key 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 |
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source of key material, you can simply generate 32 octets from it |
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and use this as your secret key. |
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|
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$public_key = Crypt::Ed25519::eddsa_public_key $secret_key |
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Takes a secret key generated by "Crypt::Ed25519::eddsa_secret_key" |
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and returns the corresponding $public_key. The derivation is |
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deterministic, i.e. the $public_key generated for a specific |
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$secret_key is always the same. |
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|
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This public key corresponds to the public key in the Ed25519 API |
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above. |
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|
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$signature = Crypt::Ed25519::eddsa_sign $message, $public_key, |
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$secret_key |
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Generates a signature for the given message using the public and |
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secret keys. Apart from specifying the $secret_key, this function is |
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identical to "Crypt::Ed25519::sign", so everything said about it is |
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true for this function as well. |
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|
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Internally, "Crypt::Ed25519::eddsa_sign" derives the corresponding |
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private key first and then calls "Crypt::Ed25519::sign", so it is |
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always slower. |
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|
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$valid = Crypt::Ed25519::eddsa_verify $message, $public_key, $signature |
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Crypt::Ed25519::eddsa_verify_croak $message, $public_key, $signature |
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Really the same as "Crypt::Ed25519::verify" and |
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"Crypt::Ed25519::verify_croak", i.e. the functions without the |
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"eddsa_" prefix. These aliases are provided so it's clear that you |
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are using EdDSA and not Ed25519 API. |
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|
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CONVERTING BETWEEN Ed25519 and EdDSA |
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The Ed25519 and EdDSA compatible APIs handle keys slightly differently: |
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The Ed25519 API gives you a public/private key pair, while EdDSA takes a |
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secret and generates a public key from it. |
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|
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You can convert an EdDSA secret to an Ed25519 private/public key pair |
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using "Crypt::Ed25519::generate_keypair": |
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|
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($public_key, $private_key) = Crypt::Ed25519::generate_keypair $secret |
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|
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As such, the EdDSA-style API allows you to store only the secret key and |
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derive the public key as needed. On the other hand, signing using the |
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private key is faster than using the secret key, so converting the |
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secret key to a public/private key pair allows you to sign a small |
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message, or many messages, faster. |
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|
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Key Exchange |
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As an extension to Ed25519, this module implements a key exchange |
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similar (But not identical) to Curve25519. For this, both sides generate |
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a keypair and send their public key to the other side. Then both sides |
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can generate the same shared secret using this function: |
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|
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$shared_secret = Crypt::Ed25519::key_exchange $other_public_key, |
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$own_private_key |
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Return the 32 octet shared secret generated from the given public |
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and private key. See SYNOPSIS for an actual example. |
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|
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SUPPORT FOR THE PERL MULTICORE SPECIFICATION |
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This module supports the perl multicore specification |
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(<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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|
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IMPLEMENTATION |
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This module currently uses "Nightcracker's Ed25519" implementation, |
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which is unmodified except for some portability fixes and static |
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delcarations, but the interface is kept implementation-agnostic to allow |
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usage of other implementations in the future. |
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|
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AUTHOR |
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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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|
