Implement KRB-FX_CF2

Draft-ietf-krb-wg-preauth-framework defines a function KRB-FX-CF2 that
combines two keys of arbitrary enctype.  Implement this function as an
exported API.

ticket: 6421

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@22094 dc483132-0cff-0310-8789-dd5450dbe970

4 files changed, 172 insertions, 0 deletions

diff --git a/src/lib/crypto/Makefile.in b/src/lib/crypto/Makefile.in
index a822e93..9454032 100644
--- a/src/lib/crypto/Makefile.in
+++ b/src/lib/crypto/Makefile.in
@@ -36,6 +36,7 @@ PROG_RPATH=$(KRB5_LIBDIR)
 STLIBOBJS=\
 	aead.o		 	\
 	block_size.o		\
+	cf2.o \
 	checksum_length.o	\
 	cksumtype_to_string.o	\
 	cksumtypes.o		\
@@ -79,6 +80,7 @@ STLIBOBJS=\
 OBJS=\
 	$(OUTPRE)aead.$(OBJEXT)		 	\
 	$(OUTPRE)block_size.$(OBJEXT)		\
+	$(OUTPRE)cf2$(OBJEXT) \
 	$(OUTPRE)checksum_length.$(OBJEXT)	\
 	$(OUTPRE)cksumtype_to_string.$(OBJEXT)	\
 	$(OUTPRE)cksumtypes.$(OBJEXT)		\
@@ -151,6 +153,7 @@ SRCS=\
 	$(srcdir)/old_api_glue.c	\
 	$(srcdir)/pbkdf2.c	\
 	$(srcdir)/prf.c \
+	$(srcdir)/cf2.c \
 	$(srcdir)/prng.c		\
 	$(srcdir)/random_to_key.c	\
 	$(srcdir)/state.c \
diff --git a/src/lib/crypto/cf2.c b/src/lib/crypto/cf2.c
new file mode 100644
index 0000000..4e25641
--- /dev/null
+++ b/src/lib/crypto/cf2.c
@@ -0,0 +1,154 @@
+/*
+ * lib/crypto/cf2.c
+ *
+ * Copyright (C) 2009 by the Massachusetts Institute of Technology.
+ * All rights reserved.
+ *
+ * Export of this software from the United States of America may
+ *   require a specific license from the United States Government.
+ *   It is the responsibility of any person or organization contemplating
+ *   export to obtain such a license before exporting.
+ * 
+ * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
+ * distribute this software and its documentation for any purpose and
+ * without fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright notice and
+ * this permission notice appear in supporting documentation, and that
+ * the name of M.I.T. not be used in advertising or publicity pertaining
+ * to distribution of the software without specific, written prior
+ * permission.  Furthermore if you modify this software you must label
+ * your software as modified software and not distribute it in such a
+ * fashion that it might be confused with the original M.I.T. software.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is" without express
+ * or implied warranty.
+ * 
+ * 
+ *
+ * Implement KRB_FX_CF2 function per
+ *draft-ietf-krb-wg-preauth-framework-09.  Take two keys and two
+ *pepper strings as input and return a combined key.
+ */
+
+#include <k5-int.h>
+#include <assert.h>
+#include "etypes.h"
+
+
+/*
+ * Call the PRF function multiple times with the pepper prefixed with
+ * a count byte  to get enough bits of output. 
+ */
+static krb5_error_code
+prf_plus( krb5_context context, krb5_keyblock *k,const char *pepper,
+	  size_t keybytes, char **out)
+{
+    krb5_error_code retval = 0;
+    size_t prflen, iterations;
+    krb5_data out_data;
+    krb5_data in_data;
+    char *buffer = NULL;
+    struct k5buf prf_inbuf;
+    krb5int_buf_init_dynamic(&prf_inbuf);
+    krb5int_buf_add_len( &prf_inbuf, "\001", 1);
+    krb5int_buf_add( &prf_inbuf, pepper);
+    retval = krb5_c_prf_length( context, k->enctype, &prflen);
+    if (retval != 0)
+	goto cleanup;
+    iterations = keybytes/prflen;
+    if ((keybytes%prflen) != 0)
+	iterations++;
+    assert(iterations <= 254);
+    buffer = malloc(iterations*prflen);
+    if (buffer == NULL) {
+	retval = ENOMEM;
+	goto cleanup;
+	}
+    if (krb5int_buf_len( &prf_inbuf) == -1) {
+	retval = ENOMEM;
+	goto cleanup;
+    }
+    in_data.length = (krb5_int32) krb5int_buf_len( &prf_inbuf);
+    in_data.data = krb5int_buf_data( &prf_inbuf);
+    out_data.length = prflen;
+    out_data.data = buffer;
+
+    while (iterations > 0) {
+	retval = krb5_c_prf( context, k, &in_data, &out_data);
+    if (retval != 0)
+	goto cleanup;
+    out_data.data += prflen;
+    in_data.data[0]++;
+    iterations--;
+    }
+ cleanup:
+    if (retval == 0 )
+	*out = buffer;
+    else{
+	if (buffer != NULL)
+	    free(buffer);
+    }
+    krb5int_free_buf( &prf_inbuf);
+    return retval;
+}
+
+    
+krb5_error_code KRB5_CALLCONV
+krb5_c_fx_cf2_simple(krb5_context context,
+		     krb5_keyblock *k1, const char *pepper1,
+		     krb5_keyblock *k2, const char *pepper2,
+		     krb5_keyblock **out)
+{
+    const struct krb5_keytypes *out_enctype;
+    size_t keybytes, keylength, i;
+    char *prf1 = NULL, *prf2 = NULL;
+    krb5_data keydata;
+    krb5_enctype out_enctype_num;
+    krb5_error_code retval = 0;
+    krb5_keyblock *out_key = NULL;
+
+
+    if (k1 == NULL ||!krb5_c_valid_enctype(k1->enctype))
+	return KRB5_BAD_ENCTYPE;
+    if (k2 == NULL || !krb5_c_valid_enctype(k2->enctype))
+	return KRB5_BAD_ENCTYPE;
+    out_enctype_num = k1->enctype;
+    assert(out != NULL);
+    assert ((out_enctype = find_enctype(out_enctype_num)) != NULL);
+    if (out_enctype->prf == NULL) {
+	if (context)
+	    krb5int_set_error(&(context->err) , KRB5_CRYPTO_INTERNAL,
+				   "Enctype %d has no PRF", out_enctype_num);
+	return KRB5_CRYPTO_INTERNAL;
+		}
+    keybytes = out_enctype->enc->keybytes;
+    keylength = out_enctype->enc->keylength;
+
+    retval = prf_plus( context, k1, pepper1, keybytes, &prf1);
+	if (retval != 0)
+	    goto cleanup;
+    retval = prf_plus( context, k2, pepper2, keybytes, &prf2);
+    if (retval != 0)
+	goto cleanup;
+    for (i = 0; i < keybytes; i++)
+	prf1[i] ^= prf2[i];
+    zap(prf2, keybytes);
+    retval = krb5int_c_init_keyblock( context, out_enctype_num, keylength, &out_key);
+    if (retval != 0)
+	goto cleanup;
+    keydata.data = prf1;
+    keydata.length = keybytes;
+    retval = out_enctype->enc->make_key( &keydata, out_key);
+
+ cleanup:
+    if (retval == 0)
+	*out = out_key;
+    else krb5int_c_free_keyblock( context, out_key);
+    if (prf1 != NULL) {
+	zap(prf1, keybytes);
+	free(prf1);
+    }
+    if (prf2 != NULL)
+	free(prf2);
+    return retval;
+}
diff --git a/src/lib/crypto/etypes.h b/src/lib/crypto/etypes.h
index 17b448c..8441fca 100644
--- a/src/lib/crypto/etypes.h
+++ b/src/lib/crypto/etypes.h
@@ -67,3 +67,17 @@ struct krb5_keytypes {
 
 extern const struct krb5_keytypes krb5_enctypes_list[];
 extern const int krb5_enctypes_length;
+
+static inline const struct krb5_keytypes*
+find_enctype (krb5_enctype enctype)
+{
+    int i;
+    for (i=0; i<krb5_enctypes_length; i++) {
+	if (krb5_enctypes_list[i].etype == enctype)
+	    break;
+    }
+
+    if (i == krb5_enctypes_length)
+	return NULL;
+    return &krb5_enctypes_list[i];
+}
diff --git a/src/lib/crypto/libk5crypto.exports b/src/lib/crypto/libk5crypto.exports
index 3cb79de..4ea46fa 100644
--- a/src/lib/crypto/libk5crypto.exports
+++ b/src/lib/crypto/libk5crypto.exports
@@ -13,6 +13,7 @@ krb5_arcfour_decrypt
 krb5_arcfour_encrypt
 krb5_arcfour_encrypt_length
 krb5_c_block_size
+krb5_c_fx_cf2_simple
 krb5_c_checksum_length
 krb5_c_crypto_length
 krb5_c_crypto_length_iov