class OpenSSL::PKey::DH

An implementation of the Diffie-Hellman key exchange protocol based on discrete logarithms in finite fields, the same basis that DSA is built on.

Accessor methods for the Diffie-Hellman parameters¶ ↑

DH#p: The prime (an OpenSSL::BN) of the Diffie-Hellman parameters.
DH#g: The generator (an OpenSSL::BN) g of the Diffie-Hellman parameters.
DH#pub_key: The per-session public key (an OpenSSL::BN) matching the private key. This needs to be passed to DH#compute_key.
DH#priv_key: The per-session private key, an OpenSSL::BN.

Example of a key exchange¶ ↑

# you may send the parameters (der) and own public key (pub1) publicly
# to the participating party
dh1 = OpenSSL::PKey::DH.new(2048)
der = dh1.to_der
pub1 = dh1.pub_key

# the other party generates its per-session key pair
dhparams = OpenSSL::PKey::DH.new(der)
dh2 = OpenSSL::PKey.generate_key(dhparams)
pub2 = dh2.pub_key

symm_key1 = dh1.compute_key(pub2)
symm_key2 = dh2.compute_key(pub1)
puts symm_key1 == symm_key2 # => true

Public Class Methods

generate(size, generator = 2) → dh

Creates a new DH instance from scratch by generating random parameters and a key pair.

size: The desired key size in bits.
generator: The generator.

# File ext/openssl/lib/openssl/pkey.rb, line 118
def generate(size, generator = 2, &blk)
  dhparams = OpenSSL::PKey.generate_parameters("DH", {
    "dh_paramgen_prime_len" => size,
    "dh_paramgen_generator" => generator,
  }, &blk)
  OpenSSL::PKey.generate_key(dhparams)
end

new → dh

new(string) → dh

new(size [, generator]) → dh

Creates a new instance of OpenSSL::PKey::DH.

If called without arguments, an empty instance without any parameter or key components is created. Use set_pqg to manually set the parameters afterwards (and optionally set_key to set private and public key components).

If a String is given, tries to parse it as a DER- or PEM- encoded parameters. See also OpenSSL::PKey.read which can parse keys of any kinds.

The DH.new(size [, generator]) form is an alias of DH.generate.

string: A String that contains the DER or PEM encoded key.
size: See DH.generate.
generator: See DH.generate.

Examples:

# Creating an instance from scratch
# Note that this is deprecated and will not work on OpenSSL 3.0 or later.
dh = OpenSSL::PKey::DH.new
dh.set_pqg(bn_p, nil, bn_g)

# Generating a parameters and a key pair
dh = OpenSSL::PKey::DH.new(2048) # An alias of OpenSSL::PKey::DH.generate(2048)

# Reading DH parameters
dh_params = OpenSSL::PKey::DH.new(File.read('parameters.pem')) # loads parameters only
dh = OpenSSL::PKey.generate_key(dh_params) # generates a key pair

static VALUE
ossl_dh_initialize(int argc, VALUE *argv, VALUE self)
{
    EVP_PKEY *pkey;
    int type;
    DH *dh;
    BIO *in = NULL;
    VALUE arg;

    TypedData_Get_Struct(self, EVP_PKEY, &ossl_evp_pkey_type, pkey);
    if (pkey)
        rb_raise(rb_eTypeError, "pkey already initialized");

    /* The DH.new(size, generator) form is handled by lib/openssl/pkey.rb */
    if (rb_scan_args(argc, argv, "01", &arg) == 0) {
        dh = DH_new();
        if (!dh)
            ossl_raise(eDHError, "DH_new");
        goto legacy;
    }

    arg = ossl_to_der_if_possible(arg);
    in = ossl_obj2bio(&arg);

    /*
     * On OpenSSL <= 1.1.1 and current versions of LibreSSL, the generic
     * routine does not support DER-encoded parameters
     */
    dh = d2i_DHparams_bio(in, NULL);
    if (dh)
        goto legacy;
    OSSL_BIO_reset(in);

    pkey = ossl_pkey_read_generic(in, Qnil);
    BIO_free(in);
    if (!pkey)
        ossl_raise(eDHError, "could not parse pkey");

    type = EVP_PKEY_base_id(pkey);
    if (type != EVP_PKEY_DH) {
        EVP_PKEY_free(pkey);
        rb_raise(eDHError, "incorrect pkey type: %s", OBJ_nid2sn(type));
    }
    RTYPEDDATA_DATA(self) = pkey;
    return self;

  legacy:
    BIO_free(in);
    pkey = EVP_PKEY_new();
    if (!pkey || EVP_PKEY_assign_DH(pkey, dh) != 1) {
        EVP_PKEY_free(pkey);
        DH_free(dh);
        ossl_raise(eDHError, "EVP_PKEY_assign_DH");
    }
    RTYPEDDATA_DATA(self) = pkey;
    return self;
}

Public Instance Methods

compute_key(pub_bn) → string

Returns a String containing a shared secret computed from the other party’s public value.

This method is provided for backwards compatibility, and calls derive internally.

Parameters¶ ↑

pub_bn is a OpenSSL::BN, not the DH instance returned by DH#public_key as that contains the DH parameters only.

# File ext/openssl/lib/openssl/pkey.rb, line 49
def compute_key(pub_bn)
  # FIXME: This is constructing an X.509 SubjectPublicKeyInfo and is very
  # inefficient
  obj = OpenSSL::ASN1.Sequence([
    OpenSSL::ASN1.Sequence([
      OpenSSL::ASN1.ObjectId("dhKeyAgreement"),
      OpenSSL::ASN1.Sequence([
        OpenSSL::ASN1.Integer(p),
        OpenSSL::ASN1.Integer(g),
      ]),
    ]),
    OpenSSL::ASN1.BitString(OpenSSL::ASN1.Integer(pub_bn).to_der),
  ])
  derive(OpenSSL::PKey.read(obj.to_der))
end

export → aString

Serializes the DH parameters to a PEM-encoding.

Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.

PEM-encoded parameters will look like:

-----BEGIN DH PARAMETERS-----
[...]
-----END DH PARAMETERS-----

See also public_to_pem (X.509 SubjectPublicKeyInfo) and private_to_pem (PKCS #8 PrivateKeyInfo or EncryptedPrivateKeyInfo) for serialization with the private or public key components.

static VALUE
ossl_dh_export(VALUE self)
{
    OSSL_3_const DH *dh;
    BIO *out;
    VALUE str;

    GetDH(self, dh);
    if (!(out = BIO_new(BIO_s_mem()))) {
        ossl_raise(eDHError, NULL);
    }
    if (!PEM_write_bio_DHparams(out, dh)) {
        BIO_free(out);
        ossl_raise(eDHError, NULL);
    }
    str = ossl_membio2str(out);

    return str;
}

Also aliased as: to_pem, to_s

generate_key! → self

Generates a private and public key unless a private key already exists. If this DH instance was generated from public DH parameters (e.g. by encoding the result of DH#public_key), then this method needs to be called first in order to generate the per-session keys before performing the actual key exchange.

Deprecated in version 3.0. This method is incompatible with OpenSSL 3.0.0 or later.

See also OpenSSL::PKey.generate_key.

Example:

# DEPRECATED USAGE: This will not work on OpenSSL 3.0 or later
dh0 = OpenSSL::PKey::DH.new(2048)
dh = dh0.public_key # #public_key only copies the DH parameters (contrary to the name)
dh.generate_key!
puts dh.private? # => true
puts dh0.pub_key == dh.pub_key #=> false

# With OpenSSL::PKey.generate_key
dh0 = OpenSSL::PKey::DH.new(2048)
dh = OpenSSL::PKey.generate_key(dh0)
puts dh0.pub_key == dh.pub_key #=> false

# File ext/openssl/lib/openssl/pkey.rb, line 91
def generate_key!
  if OpenSSL::OPENSSL_VERSION_NUMBER >= 0x30000000
    raise DHError, "OpenSSL::PKey::DH is immutable on OpenSSL 3.0; " \
    "use OpenSSL::PKey.generate_key instead"
  end

  unless priv_key
    tmp = OpenSSL::PKey.generate_key(self)
    set_key(tmp.pub_key, tmp.priv_key)
  end
  self
end

initialize_copy (p1)

HAVE_EVP_PKEY_DUP
static VALUE
ossl_dh_initialize_copy(VALUE self, VALUE other)
{
    EVP_PKEY *pkey;
    DH *dh, *dh_other;
    const BIGNUM *pub, *priv;

    TypedData_Get_Struct(self, EVP_PKEY, &ossl_evp_pkey_type, pkey);
    if (pkey)
        rb_raise(rb_eTypeError, "pkey already initialized");
    GetDH(other, dh_other);

    dh = DHparams_dup(dh_other);
    if (!dh)
        ossl_raise(eDHError, "DHparams_dup");

    DH_get0_key(dh_other, &pub, &priv);
    if (pub) {
        BIGNUM *pub2 = BN_dup(pub);
        BIGNUM *priv2 = BN_dup(priv);

        if (!pub2 || (priv && !priv2)) {
            BN_clear_free(pub2);
            BN_clear_free(priv2);
            ossl_raise(eDHError, "BN_dup");
        }
        DH_set0_key(dh, pub2, priv2);
    }

    pkey = EVP_PKEY_new();
    if (!pkey || EVP_PKEY_assign_DH(pkey, dh) != 1) {
        EVP_PKEY_free(pkey);
        DH_free(dh);
        ossl_raise(eDHError, "EVP_PKEY_assign_DH");
    }
    RTYPEDDATA_DATA(self) = pkey;
    return self;
}

params → hash

Stores all parameters of key to the hash INSECURE: PRIVATE INFORMATIONS CAN LEAK OUT!!! Don’t use :-)) (I’s up to you)

static VALUE
ossl_dh_get_params(VALUE self)
{
    OSSL_3_const DH *dh;
    VALUE hash;
    const BIGNUM *p, *q, *g, *pub_key, *priv_key;

    GetDH(self, dh);
    DH_get0_pqg(dh, &p, &q, &g);
    DH_get0_key(dh, &pub_key, &priv_key);

    hash = rb_hash_new();
    rb_hash_aset(hash, rb_str_new2("p"), ossl_bn_new(p));
    rb_hash_aset(hash, rb_str_new2("q"), ossl_bn_new(q));
    rb_hash_aset(hash, rb_str_new2("g"), ossl_bn_new(g));
    rb_hash_aset(hash, rb_str_new2("pub_key"), ossl_bn_new(pub_key));
    rb_hash_aset(hash, rb_str_new2("priv_key"), ossl_bn_new(priv_key));

    return hash;
}

params_ok? → true | false

Validates the Diffie-Hellman parameters associated with this instance. It checks whether a safe prime and a suitable generator are used. If this is not the case, false is returned.

See also the man page EVP_PKEY_param_check(3).

static VALUE
ossl_dh_check_params(VALUE self)
{
    int ret;
#ifdef HAVE_EVP_PKEY_CHECK
    EVP_PKEY *pkey;
    EVP_PKEY_CTX *pctx;

    GetPKey(self, pkey);
    pctx = EVP_PKEY_CTX_new(pkey, /* engine */NULL);
    if (!pctx)
        ossl_raise(eDHError, "EVP_PKEY_CTX_new");
    ret = EVP_PKEY_param_check(pctx);
    EVP_PKEY_CTX_free(pctx);
#else
    DH *dh;
    int codes;

    GetDH(self, dh);
    ret = DH_check(dh, &codes) == 1 && codes == 0;
#endif

    if (ret == 1)
        return Qtrue;
    else {
        /* DH_check_ex() will put error entry on failure */
        ossl_clear_error();
        return Qfalse;
    }
}

private? → true | false

Indicates whether this DH instance has a private key associated with it or not. The private key may be retrieved with DH#priv_key.

static VALUE
ossl_dh_is_private(VALUE self)
{
    OSSL_3_const DH *dh;
    const BIGNUM *bn;

    GetDH(self, dh);
    DH_get0_key(dh, NULL, &bn);

#if !defined(OPENSSL_NO_ENGINE)
    return (bn || DH_get0_engine((DH *)dh)) ? Qtrue : Qfalse;
#else
    return bn ? Qtrue : Qfalse;
#endif
}

public? → true | false

Indicates whether this DH instance has a public key associated with it or not. The public key may be retrieved with DH#pub_key.

static VALUE
ossl_dh_is_public(VALUE self)
{
    OSSL_3_const DH *dh;
    const BIGNUM *bn;

    GetDH(self, dh);
    DH_get0_key(dh, &bn, NULL);

    return bn ? Qtrue : Qfalse;
}

public_key → dhnew

Returns a new DH instance that carries just the DH parameters.

Contrary to the method name, the returned DH object contains only parameters and not the public key.

This method is provided for backwards compatibility. In most cases, there is no need to call this method.

For the purpose of re-generating the key pair while keeping the parameters, check OpenSSL::PKey.generate_key.

Example:

# OpenSSL::PKey::DH.generate by default generates a random key pair
dh1 = OpenSSL::PKey::DH.generate(2048)
p dh1.priv_key #=> #<OpenSSL::BN 1288347...>
dhcopy = dh1.public_key
p dhcopy.priv_key #=> nil

# File ext/openssl/lib/openssl/pkey.rb, line 33
def public_key
  DH.new(to_der)
end

set_key(pub_key, priv_key) → self

Sets pub_key and priv_key for the DH instance. priv_key may be nil.

set_pqg(p, q, g) → self

Sets p, q, g to the DH instance.

to_der → aString

Serializes the DH parameters to a DER-encoding

Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.

See also public_to_der (X.509 SubjectPublicKeyInfo) and private_to_der (PKCS #8 PrivateKeyInfo or EncryptedPrivateKeyInfo) for serialization with the private or public key components.

static VALUE
ossl_dh_to_der(VALUE self)
{
    OSSL_3_const DH *dh;
    unsigned char *p;
    long len;
    VALUE str;

    GetDH(self, dh);
    if((len = i2d_DHparams(dh, NULL)) <= 0)
        ossl_raise(eDHError, NULL);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if(i2d_DHparams(dh, &p) < 0)
        ossl_raise(eDHError, NULL);
    ossl_str_adjust(str, p);

    return str;
}

to_pem → aString

Serializes the DH parameters to a PEM-encoding.

Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.

PEM-encoded parameters will look like:

-----BEGIN DH PARAMETERS-----
[...]
-----END DH PARAMETERS-----

See also public_to_pem (X.509 SubjectPublicKeyInfo) and private_to_pem (PKCS #8 PrivateKeyInfo or EncryptedPrivateKeyInfo) for serialization with the private or public key components.

Alias for: export

to_s → aString

Serializes the DH parameters to a PEM-encoding.

Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.

PEM-encoded parameters will look like:

-----BEGIN DH PARAMETERS-----
[...]
-----END DH PARAMETERS-----

See also public_to_pem (X.509 SubjectPublicKeyInfo) and private_to_pem (PKCS #8 PrivateKeyInfo or EncryptedPrivateKeyInfo) for serialization with the private or public key components.

Alias for: export