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 #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 #to_pem or #to_der the result will
not contain a public/private key pair yet. This needs to
be generated using #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 (FIXNUM_P(arg)) { if (!NIL_P(gen)) { g = NUM2INT(gen); } if (!(dh = dh_generate(FIX2INT(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 the DH instance returned by
#public_key as that contains the DH parameters only.
static VALUE ossl_dh_compute_key(VALUE self, VALUE pub) { DH *dh; EVP_PKEY *pkey; BIGNUM *pub_key; VALUE str; int len; GetPKeyDH(self, pkey); dh = pkey->pkey.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) { EVP_PKEY *pkey; BIO *out; VALUE str; GetPKeyDH(self, pkey); if (!(out = BIO_new(BIO_s_mem()))) { ossl_raise(eDHError, NULL); } if (!PEM_write_bio_DHparams(out, pkey->pkey.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 #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; EVP_PKEY *pkey; GetPKeyDH(self, pkey); dh = pkey->pkey.dh; if (!DH_generate_key(dh)) ossl_raise(eDHError, "Failed to generate key"); 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) { EVP_PKEY *pkey; VALUE hash; GetPKeyDH(self, pkey); hash = rb_hash_new(); rb_hash_aset(hash, rb_str_new2("p"), ossl_bn_new(pkey->pkey.dh->p)); rb_hash_aset(hash, rb_str_new2("g"), ossl_bn_new(pkey->pkey.dh->g)); rb_hash_aset(hash, rb_str_new2("pub_key"), ossl_bn_new(pkey->pkey.dh->pub_key)); rb_hash_aset(hash, rb_str_new2("priv_key"), ossl_bn_new(pkey->pkey.dh->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; EVP_PKEY *pkey; int codes; GetPKeyDH(self, pkey); dh = pkey->pkey.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) { EVP_PKEY *pkey; GetPKeyDH(self, pkey); return (DH_PRIVATE(pkey->pkey.dh)) ? Qtrue : Qfalse; }
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) { EVP_PKEY *pkey; GetPKeyDH(self, pkey); return (pkey->pkey.dh->pub_key) ? 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 #generate_key!. The
“public key” needed for a key exchange with #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 #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) { EVP_PKEY *pkey; DH *dh; VALUE obj; GetPKeyDH(self, pkey); dh = DHparams_dup(pkey->pkey.dh); /* err check perfomed by dh_instance */ obj = dh_instance(CLASS_OF(self), dh); if (obj == Qfalse) { DH_free(dh); ossl_raise(eDHError, NULL); } return obj; }
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) { EVP_PKEY *pkey; unsigned char *p; long len; VALUE str; GetPKeyDH(self, pkey); if((len = i2d_DHparams(pkey->pkey.dh, NULL)) <= 0) ossl_raise(eDHError, NULL); str = rb_str_new(0, len); p = (unsigned char *)RSTRING_PTR(str); if(i2d_DHparams(pkey->pkey.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) { EVP_PKEY *pkey; BIO *out; VALUE str; GetPKeyDH(self, pkey); if (!(out = BIO_new(BIO_s_mem()))) { ossl_raise(eDHError, NULL); } if (!DHparams_print(out, pkey->pkey.dh)) { BIO_free(out); ossl_raise(eDHError, NULL); } str = ossl_membio2str(out); return str; }