Not Recommended For New Applications: Use pynacl Instead
For new applications, I recommend you use
pynacl instead of this repository.
PyNaCl is larger and takes longer to build (it contains the complete
NaCl/libsodium library, not just the ed25519 portion), but it is
well-maintained by the diligent and conscientious PyCA team, whereas I've
allowed this repository to languish.
PyNaCl is also about 10-20 times
faster. A guide for migration fron
PyNaCl is included
Python Bindings to the Ed25519 Digital Signature System
This package provides python bindings to a C implementation of the Ed25519 public-key signature system 1. The C code is copied from the SUPERCOP benchmark suite 2, using the portable "ref" implementation (not the high-performance assembly code), and is very similar to the copy in the NaCl library 3. The C code is in the public domain 4. This python binding is released under the MIT license (see LICENSE in this distribution).
With this library, you can quickly (2ms) create signing+verifying keypairs, derive a verifying key from a signing key, sign messages, and verify the signatures. The keys and signatures are very short, making them easy to handle and incorporate into other protocols. All known attacks take at least 2^128 operations, providing the same security level as AES-128, NIST P-256, and RSA-3072.
This library includes a copy of all the C code necessary. You will need Python 2.7 or Python 3.x (3.4 or later) and a C compiler. The tests are run automatically against python 2.7, 3.4, 3.5, 3.6, 3.7, and pypy versions of Python 2.7 and 3.6.
Speed and Key Sizes
Signing key seeds are merely 32 bytes of random data, so generating a signing key is trivial. Deriving a public verifying key takes more time, as do the actual signing and verifying operations.
On my 2010-era Mac laptop (2.8GHz Core2Duo), deriving a verifying key takes 1.9ms, signing takes 1.9ms, and verification takes 6.3ms.
Ed25519 private signing keys are 32 bytes long (this seed is expanded to 64 bytes when necessary). The public verifying keys are also 32 bytes long. Signatures are 64 bytes long. All operations provide a 128-bit security level.
The Ed25519 web site includes a (spectacularly slow) pure-python implementation for educational purposes. That code includes a set of known-answer-tests. Those tests are included in this distribution, and takes about 17 seconds to execute. The distribution also includes unit tests of the object-oriented SigningKey / VerifyingKey layer. Run test.py to execute these tests.
The Ed25519 algorithm and C implementation are carefully designed to prevent timing attacks. The Python wrapper might not preserve this property. Until it has been audited for this purpose, do not allow attackers to measure how long it takes you to generate a keypair or sign a message. Key generation depends upon a strong source of random numbers. Do not use it on a system where os.urandom() is weak.
Unlike typical DSA/ECDSA algorithms, signing does not require a source of entropy. Ed25519 signatures are deterministic: using the same key to sign the same data any number of times will result in the same signature each time.
To build and install the library, run the normal setup.py command:
python setup.py build sudo python setup.py install
You can run the (fast) test suite, the (slower) known-answer-tests, and the speed-benchmarks through setup.py commands too:
python setup.py test python setup.py test_kat python setup.py speed
Prefixes and Encodings
The basic keypair/sign/verify operations work on binary bytestrings: signing keys are created with a 32-byte seed or a 64-byte expanded form, verifying keys are serialized as 32-byte binary strings, and signatures are 64-byte binary strings.
All methods that generate or accept bytestrings take a prefix= argument, which is simply prepended to the output or stripped from the input. This can be used for a cheap version check: if you use e.g. prefix="pubkey0-" when handling verifying keys, and later update your application to use a different kind of key (and update to "pubkey1-"), then older receivers will throw a clean error when faced with a key format that they cannot handle.
These methods also accept an encoding= argument, which makes them return an ASCII string instead of a binary bytestring. This makes it convenient to display verifying keys or signatures to cut-and-paste or encode into JSON messages. Be careful when encouraging users to cut-and-paste signing keys, since you might enable them to accidentally reveal those keys: in general, it should require slightly more attention to handle signing keys than verifying keys.
encoding= can be set to one of "base64", "base32", "base16", or "hex" (an alias for "base16"). The strings are stripped of trailing "=" markers and lowercased (for base32/base16).
The first step is to create a signing key and store it. The safest way to generate a key is with the create_keypair() function, which uses 32 bytes of random data from os.urandom() (although you can provide an alternative entropy source with the entropy= argument):
import ed25519 signing_key, verifying_key = ed25519.create_keypair() open("my-secret-key","wb").write(signing_key.to_bytes()) vkey_hex = verifying_key.to_ascii(encoding="hex") print "the public key is", vkey_hex
The private signing key string produced by to_bytes() is 64 bytes long, and includes a copy of the public key (to avoid the 1.9ms needed to recalculate it later). If you want to store less data (and recompute the public key later), you can store just the 32 byte seed instead:
The signing key is an instance of the ed25519.SigningKey class. To
reconstruct this instance from a serialized form, the constructor accepts the
output of either
keydata = open("my-secret-key","rb").read() signing_key = ed25519.SigningKey(keydata) seed = open("my-secret-seed","rb").read() signing_key2 = ed25519.SigningKey(seed) assert signing_key == signing_key2
Special-purpose applications may want to derive keypairs from existing secrets; any 32-byte uniformly-distributed random string can be provided as a seed:
import os, hashlib master = os.urandom(87) seed = hashlib.sha256(master).digest() signing_key = ed25519.SigningKey(seed)
Once you have the SigningKey instance, use its .sign() method to sign a message. The signature is 64 bytes, but can be generated in printable form with the encoding= argument:
sig = signing_key.sign(b"hello world", encoding="base64") print "sig is:", sig
On the verifying side, the receiver first needs to construct a ed25519.VerifyingKey instance from the serialized string, then use its .verify() method on the signature and message:
vkey_hex = b"1246b84985e1ab5f83f4ec2bdf271114666fd3d9e24d12981a3c861b9ed523c6" verifying_key = ed25519.VerifyingKey(vkey_hex, encoding="hex") try: verifying_key.verify(sig, b"hello world", encoding="base64") print "signature is good" except ed25519.BadSignatureError: print "signature is bad!"
If you happen to have the SigningKey but not the corresponding VerifyingKey,
you can derive it with
.get_verifying_key(). This allows the sending side to
hold just 32 bytes of data and derive everything else from that:
keydata = open("my-secret-seed","rb").read() signing_key = ed25519.SigningKey(keydata) verifying_key = signing_key.get_verifying_key()
There is also a basic command-line keygen/sign/verify tool in bin/edsig .
The complete API is summarized here:
sk,vk = ed25519.create_keypair(entropy=os.urandom) vk = sk.get_verifying_key() signature = sk.sign(message, prefix=, encoding=) vk.verify(signature, message, prefix=, encoding=) seed = sk.to_seed(prefix=) sk = SigningKey(seed, prefix=) bytes = sk.to_bytes(prefix=) sk = SigningKey(bytes, prefix=) ascii = sk.to_ascii(prefix=, encoding=) # encodes seed sk = SigningKey(ascii, prefix=, encoding=) bytes = vk.to_bytes(prefix=) vk = VerifyingKey(bytes, prefix=) ascii = vk.to_ascii(prefix=, encoding=) vk = VerifyingKey(ascii, prefix=, encoding=)
Migrating To pynacl
PyNaCl has a similar workflow: there are
objects, and you can obtain the verifier from the signer. But the API is
python-ed25519 | PyNaCl | import ed25519 import (create_keypair, | from nacl.signing import SigningKey, VerifyKey SigningKey, VerifyingKey) | from nacl.encoding import HexEncoder | sk,vk = ed25519.create_keypair() | sk = SigningKey.generate() vk = sk.get_verifying_key() | vk = sk.verify_key | sig = sk.sign(message) | sig = sk.sign(message).signature vk.verify(sig, message) | msg = vk.verify(message, sig) # returns None or raises | # returns message or raises # ed25519.BadSignatureError | # nacl.exceptions.BadSignatureError | sm = sk.sign(message)+message | sm = sk.sign(message) vk.verify(sm[:64], sm[64:]) | msg = vk.verify(sm) msg = sm[64:] | | seed = sk.to_seed() | seed = sk.encode() sk = SigningKey(seed) | sk = SigningKey(seed) bytes = sk.to_bytes() | no equivalent sk = SigningKey(bytes) | no equivalent hex = sk.to_ascii(encoding='hex') | hex = sk.encode(HexEncoder()) sk = SigningKey(hex, encoding='hex') | sk = SigningKey(hex, HexEncoder()) | bytes = vk.to_bytes() | bytes = vk.encode() vk = VerifyingKey(bytes) | vk = VerifyKey(bytes) hex = vk.to_ascii(encoding='hex') | hex = vk.encode(HexEncoder()) vk = VerifyingKey(hex, encoding='hex') | vk = VerifyKey(hex, HexEncoder)
PyNaCl API has no equivalent of
SigningKey.to_bytes (which returns
the expanded internal 64-byte form of the private key). Instead, it only
offers a way to get the 32-byte seed from which the expanded form is derived.
The seed takes slightly more time to expand whenever a
SigningKey object is
created, but in practice the difference is trivial.
It also doesn't include
prefix= argument, which can be
used to prepend/require/strip a short string (e.g.
pubkey-v1-) in the front
of each serialized key. These prefixes could be used to detect errors in
which the wrong kind of string was used to build a
VerifyingKey object, but this functionality is easy to add on top of the
sig = sk.sign(message) returns 64 bytes with just the
detached signature, and
vk.verify(sig, message) must be given both this
signature and the original message, as two separate arguments. As a result,
when you send the signed message over a network message or store it in a
file, you must deliver two things, not just one. The verifier either returns
None or throws an exception.
sm = sk.sign(message) returns a special
SignedMessage object. This inherits from the standard
bytes type, and
when you treat it as bytes, it contains the concatenation of the signature
followed by the original message. In this form, you only have to deliver one
thing over the wire. But it also has two special attributes:
contains just the 64-byte detached signature, and
sm.message contains just
the original message.
vk.verify() can either accept a single
bytes containing the
concatenated signature+message as
vk.verify(sm) (which is the equivalent of
vk.verify(sm.signature+sm.message)), or it can accept them separately as
vk.verify(message, sig) (note the inversion of arguments compared to
python-ed25519). In either case,
vk.verify() returns the original
message, or throws an exception.
In many cases, passing a composite "signed message" object over the wire is
safer. This approach encourages a mindset in which there are two distinct
types of objects: opaque signed things and unsigned bytes. The
vk.verify() functions convert one type into the other, and there is no
way to even look at the message bytes until you pass it through the
verification function. This reduces the temptation to let your program act
upon unverified data. Compare this against the less-safe
API, which makes it possible to comment out the signature verification
(perhaps while debugging something) and still have an apparently-functional
but now-fatally-insecure program.
On the other hand, there are situations where you need a detached signature
on some pre-existing object. Perhaps you have multiple parties all signing
the same thing in parallel. Or you have a transport protocol in which the
signature is computed over a combination of locally-managed sequence numbers
and actual payloads from the network. In these cases you can use
sm.signature attribute and the two-argument form of