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 toDH#compute_key
. - DH#priv_key
-
The per-session private key, an
OpenSSL::BN
.
Example of a key exchange¶ ↑
dh1 = OpenSSL::PKey::DH.new(2048) der = dh1.public_key.to_der #you may send this publicly to the participating party dh2 = OpenSSL::PKey::DH.new(der) dh2.generate_key! #generate the per-session key pair symm_key1 = dh1.compute_key(dh2.pub_key) symm_key2 = dh2.compute_key(dh1.pub_key) puts symm_key1 == symm_key2 # => true
Public Class Methods
Creates a new DH
instance from scratch by generating the private and public components alike.
Parameters¶ ↑
-
size is an integer representing the desired key size. Keys smaller than 1024 bits should be considered insecure.
-
generator is a small number > 1, typically 2 or 5.
static VALUE ossl_dh_s_generate(int argc, VALUE *argv, VALUE klass) { DH *dh ; int g = 2; VALUE size, gen, obj; if (rb_scan_args(argc, argv, "11", &size, &gen) == 2) { g = NUM2INT(gen); } dh = dh_generate(NUM2INT(size), g); obj = dh_instance(klass, dh); if (obj == Qfalse) { DH_free(dh); ossl_raise(eDHError, NULL); } return obj; }
Either generates a DH
instance from scratch or by reading already existing DH
parameters from string. Note that when reading a DH
instance from data that was encoded from a DH
instance by using DH#to_pem
or DH#to_der
the result will not contain a public/private key pair yet. This needs to be generated using DH#generate_key!
first.
Parameters¶ ↑
-
size is an integer representing the desired key size. Keys smaller than 1024 bits should be considered insecure.
-
generator is a small number > 1, typically 2 or 5.
-
string contains the DER or PEM encoded key.
Examples¶ ↑
DH.new # -> dh DH.new(1024) # -> dh DH.new(1024, 5) # -> dh #Reading DH parameters dh = DH.new(File.read('parameters.pem')) # -> dh, but no public/private key yet dh.generate_key! # -> dh with public and private key
static VALUE ossl_dh_initialize(int argc, VALUE *argv, VALUE self) { EVP_PKEY *pkey; DH *dh; int g = 2; BIO *in; VALUE arg, gen; GetPKey(self, pkey); if(rb_scan_args(argc, argv, "02", &arg, &gen) == 0) { dh = DH_new(); } else if (RB_INTEGER_TYPE_P(arg)) { if (!NIL_P(gen)) { g = NUM2INT(gen); } if (!(dh = dh_generate(NUM2INT(arg), g))) { ossl_raise(eDHError, NULL); } } else { arg = ossl_to_der_if_possible(arg); in = ossl_obj2bio(&arg); dh = PEM_read_bio_DHparams(in, NULL, NULL, NULL); if (!dh){ OSSL_BIO_reset(in); dh = d2i_DHparams_bio(in, NULL); } BIO_free(in); if (!dh) { ossl_raise(eDHError, NULL); } } if (!EVP_PKEY_assign_DH(pkey, dh)) { DH_free(dh); ossl_raise(eDHError, NULL); } return self; }
Public Instance Methods
Returns a String
containing a shared secret computed from the other party's public value. See DH_compute_key() for further information.
Parameters¶ ↑
-
pub_bn is a
OpenSSL::BN
, not theDH
instance returned byDH#public_key
as that contains theDH
parameters only.
static VALUE ossl_dh_compute_key(VALUE self, VALUE pub) { DH *dh; const BIGNUM *pub_key, *dh_p; VALUE str; int len; GetDH(self, dh); DH_get0_pqg(dh, &dh_p, NULL, NULL); if (!dh_p) ossl_raise(eDHError, "incomplete DH"); pub_key = GetBNPtr(pub); len = DH_size(dh); str = rb_str_new(0, len); if ((len = DH_compute_key((unsigned char *)RSTRING_PTR(str), pub_key, dh)) < 0) { ossl_raise(eDHError, NULL); } rb_str_set_len(str, len); return str; }
Encodes this DH
to its PEM encoding. Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.
static VALUE ossl_dh_export(VALUE self) { 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; }
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.
Example¶ ↑
dh = OpenSSL::PKey::DH.new(2048) public_key = dh.public_key #contains no private/public key yet public_key.generate_key! puts public_key.private? # => true
static VALUE ossl_dh_generate_key(VALUE self) { DH *dh; GetDH(self, dh); if (!DH_generate_key(dh)) ossl_raise(eDHError, "Failed to generate key"); return self; }
static VALUE ossl_dh_initialize_copy(VALUE self, VALUE other) { EVP_PKEY *pkey; DH *dh, *dh_other; const BIGNUM *pub, *priv; GetPKey(self, pkey); if (EVP_PKEY_base_id(pkey) != EVP_PKEY_NONE) ossl_raise(eDHError, "DH already initialized"); GetDH(other, dh_other); dh = DHparams_dup(dh_other); if (!dh) ossl_raise(eDHError, "DHparams_dup"); EVP_PKEY_assign_DH(pkey, dh); 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); } return self; }
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) { 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; }
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.
static VALUE ossl_dh_check_params(VALUE self) { DH *dh; int codes; GetDH(self, dh); if (!DH_check(dh, &codes)) { return Qfalse; } return codes == 0 ? Qtrue : Qfalse; }
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) { 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)) ? Qtrue : Qfalse; #else return bn ? Qtrue : Qfalse; #endif }
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) { DH *dh; const BIGNUM *bn; GetDH(self, dh); DH_get0_key(dh, &bn, NULL); return bn ? Qtrue : Qfalse; }
Returns a new DH
instance that carries just the public information, i.e. the prime p and the generator g, but no public/private key yet. Such a pair may be generated using DH#generate_key!
. The “public key” needed for a key exchange with DH#compute_key
is considered as per-session information and may be retrieved with DH#pub_key once a key pair has been generated. If the current instance already contains private information (and thus a valid public/private key pair), this information will no longer be present in the new instance generated by DH#public_key
. This feature is helpful for publishing the Diffie-Hellman parameters without leaking any of the private per-session information.
Example¶ ↑
dh = OpenSSL::PKey::DH.new(2048) # has public and private key set public_key = dh.public_key # contains only prime and generator parameters = public_key.to_der # it's safe to publish this
static VALUE ossl_dh_to_public_key(VALUE self) { DH *orig_dh, *dh; VALUE obj; GetDH(self, orig_dh); dh = DHparams_dup(orig_dh); /* err check perfomed by dh_instance */ obj = dh_instance(rb_obj_class(self), dh); if (obj == Qfalse) { DH_free(dh); ossl_raise(eDHError, NULL); } return obj; }
Sets pub_key and priv_key for the DH
instance. priv_key may be nil
.
Sets p, q, g to the DH
instance.
Encodes this DH
to its DER encoding. Note that any existing per-session public/private keys will not get encoded, just the Diffie-Hellman parameters will be encoded.
static VALUE ossl_dh_to_der(VALUE self) { 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; }
Prints all parameters of key to buffer INSECURE: PRIVATE INFORMATIONS CAN LEAK OUT!!! Don't use :-)) (I's up to you)
static VALUE ossl_dh_to_text(VALUE self) { DH *dh; BIO *out; VALUE str; GetDH(self, dh); if (!(out = BIO_new(BIO_s_mem()))) { ossl_raise(eDHError, NULL); } if (!DHparams_print(out, dh)) { BIO_free(out); ossl_raise(eDHError, NULL); } str = ossl_membio2str(out); return str; }