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  • openssl/ossl_pkey.c

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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

generate(size [, generator]) → dh click to toggle source

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;
}
            
new([size [, generator] | string]) → dh click to toggle source

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

compute_key(pub_bn) → aString click to toggle source

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;
}
            
to_pem → aString click to toggle source

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;
}
            
Also aliased as: to_pem, to_s
generate_key! → self click to toggle source

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;
}
            
params → hash click to toggle source

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;
}
            
check_params → true | false click to toggle source

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;
}
            
private? → true | false click to toggle source

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;
}
            
public? → true | false click to toggle source

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;
}
            
public_key → aDH click to toggle source

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;
}
            
to_der → aString click to toggle source

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;
}
            
to_pem() click to toggle source
Alias for: export
to_s() click to toggle source
Alias for: export
to_text → aString click to toggle source

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;
}
            

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