Openssl Generate Strong Keys Using Eecdh

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  1. Openssl Dh Key
  2. Openssl Generate Strong Keys Using Ecdh Key
  • Command Line Elliptic Curve Operations. OpenSSL provides two command line tools for working with keys suitable for Elliptic Curve (EC) algorithms: The only Elliptic Curve algorithms that OpenSSL currently supports are Elliptic Curve Diffie Hellman (ECDH) for key agreement and Elliptic Curve Digital Signature Algorithm (ECDSA) for signing/verifying.
  • How to generate RSA and EC keys with OpenSSL. How to generate keys in PEM format using the OpenSSL command line tools? The JOSE standard recommends a minimum RSA key size of 2048 bits. To generate a 2048-bit RSA private + public key pair for use in RSxxx and PSxxx signatures.

The code in this repo relies on OpenSSL's C code library and command line tool. The commands in this README.md mirror the same function as the C code but use OpenSSL's command line tool. The C code represents my User 1 and the command line pieces represent User 2. This is useful as it helps demo how ECDH works and validates that both sides are deriving the same key. NOTE - the HMAC operation, after the ECDH piece has completed, has been verified against https://tools.ietf.org/html/rfc4231

Background - Diffie-Hellman

Reasons for importing keys include wanting to make a backup of a private key (generated keys are non-exportable, for security reasons), or if the private key is provided by an external source. This document will guide you through using the OpenSSL command line tool to generate a key pair which you can then import into a YubiKey. Jan 26, 2017  To generate a ECDH key pair (not a DH key pair), with the OpenSSL command-line tool you must first select one of the available curves. A named curve is simply a well defined and well known set of parameters that define an elliptic curve. Print them here: openssl ecparam -listcurves. User 1: Setup is all done in C code.

Diffie-Hellman is a Key Agreement protocol. It is used when two parties want to derive the same shared secret over an insecure channel. The secret key cannot be observed by intercepting the communication between the two parties.

  • Each party MUST share their own EC Public Key with the other party.
  • Each party MUST agree on the Named Curved being used before generating the EC Key Pair.
  • The two parties NEVER exchange the derived key.

Background - Diffie-Hellman alone is not enough

Diffie-Hellman provides no mechanism for ensuring that the entity on the other end of the connection is who you think it is. For mobile apps, this is where the value of other Data in Transit controls such as Certificate Pinning, HTTP Basic Auth, Access Token schemes come into play.

Background - Why use ECDH?

Elliptic Curve Diffie-Hellman (ECDH) is an Elliptic Curve variant of the standard Diffie Hellman algorithm. I like it over traditional DH which uses RSA for two reasons:

  • Key generation is quicker. This is important for mobile apps when you might rotate your keys or even generate new EC Key Pairs for each session.
  • A slightly simpler Key Derivation process. You only need the other side's Public Key as you both have already agreed on a Named Curve [and the parameters to use in Key Generation].

Setup OpenSSL's Command Line Tool

Print version (and All information) regarding OpenSSL install

openssl version -a

This will spit out your version which is likely to look like:

Game activate keys bitcoin generator hack. OpenSSL 1.0.2h 3 May 2016

Find out where it located on your machine:which openssl

Smoke test it works:openssl

and then type:speed

Select a well known, well tested Curve

To generate a ECDH key pair (not a DH key pair), with the OpenSSL command-line tool you must first select one of the available curves. A named curve is simply a well defined and well known set of parameters that define an elliptic curve.

Print them here:

openssl ecparam -list_curves

User 1: Setup is all done in C code

Generate a ECDH Key Pair in C code based on the selected Curve. Just build run the C code. It will create the required PEM files.

Checkpoints

Ok, the OpenSSL list is very misleading. Better read this [article] for the actual truth. Now generate a curve PEM file:

openssl ecparam -out ec_param.pem -name prime256v1

Check the curve was ok.openssl ecparam -in secp256k1.pem -text -check

This will print something like:ASN1 OID: prime256v1NIST CURVE: P-256

Note - you cannot put a key file into this command.

Checkpoint: Print out the C code

Print out the C code that was used to generate the EC Parameters.

openssl ecparam -in ec_param.pem -text -C

User 2: Setup

Generate a ECDH Key Pair and state Explicit parameters.

openssl ecparam -in ec_paramprime256v1.pem -genkey -noout -out appKey.pem -param_enc explicit

Now you can read the Public, Private and Named Curve by typing:openssl pkey -in appKey.pem -text -noout

Now extract the public key in preparation for sharing.openssl pkey -in appKey.pem -pubout -out appPubKey.pem

Checkpoint: Check your Key Pair, Public Key

Print the newly extracted public key.openssl ec -in appPubKey.pem -pubin -text -noout

Note - iIt will tell you the Private Key Length (256 bit).

A slightly abbreviated version (due to compression) is:openssl ec -in appPubKey.pem -pubin -text -noout -conv_form compressed

Checkpoint: Check your Key Pair, Private Key

Check your EC Private Key details by typing the following command.openssl pkey -in appKey.pem -text -noout

Notice the Private Key elements that are excluded from the public key file.

User 2: get Server’s Public Key

This is the tricker piece. As it requires a login and callback. Stubbed for now.

User 2: attempt to generate the Secret Key

The magic step.
openssl pkeyutl -derive -inkey appKey.pem -peerkey serPubKey.pem -out appBinaryKey.bin

Print the binary secret key into hex.xxd appBinaryKey.bin

Checkpoint - almost there - Keys must be equal

If your keys match, you can perform the last step. The Hmac.

Now add Authenticity to your Derived Secret

This step assumes both parties shared - out of band - a shared key that is used to create a Keyed-hash (mac).$ openssl dgst -sha256 -mac HMAC -macopt hexkey:0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b appSecret.bin

Openssl Dh Key

Final test to ensure keys match

$ cmp secret1.bin secret2.bin

Checkpoint : make keys readable

Convert the binary key to a b64 keyopenssl base64 -in serBinaryKey.bin -out serB64Key.txt

Openssl Generate Strong Keys Using Ecdh Key

You don’t need the following step but it shows the step is reversible$ openssl base64 -d -in secret1.b64 -out secret3.bin