xref: /illumos-gate/usr/src/uts/common/gssapi/mechs/krb5/crypto/dk/dk_decrypt.c (revision 55fea89dcaa64928bed4327112404dcb3e07b79f)
1 /*
2  * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
3  * Use is subject to license terms.
4  */
5 
6 
7 /*
8  * Copyright (C) 1998 by the FundsXpress, INC.
9  *
10  * All rights reserved.
11  *
12  * Export of this software from the United States of America may require
13  * a specific license from the United States Government.  It is the
14  * responsibility of any person or organization contemplating export to
15  * obtain such a license before exporting.
16  *
17  * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
18  * distribute this software and its documentation for any purpose and
19  * without fee is hereby granted, provided that the above copyright
20  * notice appear in all copies and that both that copyright notice and
21  * this permission notice appear in supporting documentation, and that
22  * the name of FundsXpress. not be used in advertising or publicity pertaining
23  * to distribution of the software without specific, written prior
24  * permission.  FundsXpress makes no representations about the suitability of
25  * this software for any purpose.  It is provided "as is" without express
26  * or implied warranty.
27  *
28  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
29  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
30  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
31  */
32 
33 #include "k5-int.h"
34 #include "dk.h"
35 
36 #define K5CLENGTH 5 /* 32 bit net byte order integer + one byte seed */
37 
38 static krb5_error_code
39 krb5_dk_decrypt_maybe_trunc_hmac(krb5_context context,
40 				 const struct krb5_enc_provider *enc,
41 				 const struct krb5_hash_provider *hash,
42 				 const krb5_keyblock *key,
43 				 krb5_keyusage usage,
44 				 const krb5_data *ivec,
45 				 const krb5_data *input,
46 				 krb5_data *output,
47 				 size_t hmacsize);
48 
49 krb5_error_code
krb5_dk_decrypt(krb5_context context,const struct krb5_enc_provider * enc,const struct krb5_hash_provider * hash,const krb5_keyblock * key,krb5_keyusage usage,const krb5_data * ivec,const krb5_data * input,krb5_data * output)50 krb5_dk_decrypt(
51 		krb5_context context,
52 		const struct krb5_enc_provider *enc,
53 		const struct krb5_hash_provider *hash,
54 		const krb5_keyblock *key, krb5_keyusage usage,
55 		const krb5_data *ivec, const krb5_data *input,
56 		krb5_data *output)
57 {
58     return krb5_dk_decrypt_maybe_trunc_hmac(context, enc, hash, key, usage,
59 					    ivec, input, output, 0);
60 }
61 
62 krb5_error_code
krb5int_aes_dk_decrypt(krb5_context context,const struct krb5_enc_provider * enc,const struct krb5_hash_provider * hash,const krb5_keyblock * key,krb5_keyusage usage,const krb5_data * ivec,const krb5_data * input,krb5_data * output)63 krb5int_aes_dk_decrypt(
64 		       krb5_context context,
65 		       const struct krb5_enc_provider *enc,
66 		       const struct krb5_hash_provider *hash,
67 		       const krb5_keyblock *key, krb5_keyusage usage,
68 		       const krb5_data *ivec, const krb5_data *input,
69 		       krb5_data *output)
70 {
71     return krb5_dk_decrypt_maybe_trunc_hmac(context, enc, hash, key, usage,
72 					    ivec, input, output, 96 / 8);
73 }
74 
75 static krb5_error_code
krb5_dk_decrypt_maybe_trunc_hmac(krb5_context context,const struct krb5_enc_provider * enc,const struct krb5_hash_provider * hash,const krb5_keyblock * key,krb5_keyusage usage,const krb5_data * ivec,const krb5_data * input,krb5_data * output,size_t hmacsize)76 krb5_dk_decrypt_maybe_trunc_hmac(
77 				 krb5_context context,
78 				 const struct krb5_enc_provider *enc,
79 				 const struct krb5_hash_provider *hash,
80 				 const krb5_keyblock *key, krb5_keyusage usage,
81 				 const krb5_data *ivec, const krb5_data *input,
82 				 krb5_data *output, size_t hmacsize)
83 {
84     krb5_error_code ret;
85     size_t hashsize, blocksize, enclen, plainlen;
86     unsigned char *plaindata = NULL, *cksum = NULL, *cn;
87     krb5_data d1, d2;
88     krb5_keyblock *derived_encr_key = NULL;
89     krb5_keyblock *derived_hmac_key = NULL;
90 
91     KRB5_LOG0(KRB5_INFO, "krb5_dk_decrypt() start\n");
92 
93     /*
94      * Derive the encryption and hmac keys.
95      * This routine is optimized to fetch the DK
96      * from the original key's DK list.
97      */
98     ret = init_derived_keydata(context, enc,
99 			    (krb5_keyblock *)key,
100 			    usage,
101 			    &derived_encr_key,
102 			    &derived_hmac_key);
103     if (ret)
104 	    return (ret);
105 
106     hashsize = hash->hashsize;
107     blocksize = enc->block_size;
108 
109     if (hmacsize == 0)
110 	hmacsize = hashsize;
111     else if (hmacsize > hashsize)
112 	return (KRB5KRB_AP_ERR_BAD_INTEGRITY);
113 
114     /* Verify input and output lengths. */
115     if (input->length < blocksize + hmacsize)
116         return KRB5_BAD_MSIZE;
117     if (output->length < input->length - blocksize - hmacsize)
118         return KRB5_BAD_MSIZE;
119 
120     enclen = input->length - hmacsize;
121 
122     if ((plaindata = (unsigned char *) MALLOC(enclen)) == NULL) {
123 	    ret = ENOMEM;
124 	    goto cleanup;
125     }
126 
127     /* decrypt the ciphertext */
128 
129     d1.length = enclen;
130     d1.data = input->data;
131 
132     d2.length = enclen;
133     d2.data = (char *) plaindata;
134 
135     if ((ret = ((*(enc->decrypt))(context, derived_encr_key,
136 			ivec, &d1, &d2))) != 0)
137 	goto cleanup;
138 
139     if (ivec != NULL && ivec->length == blocksize) {
140 	cn = (unsigned char *) d1.data + d1.length - blocksize;
141     } else {
142 	cn = NULL;
143     }
144 
145     /* verify the hash */
146 
147     if ((cksum = (unsigned char *) MALLOC(hashsize)) == NULL) {
148 	    ret = ENOMEM;
149 	    goto cleanup;
150     }
151     d1.length = hashsize;
152     d1.data = (char *) cksum;
153 
154 #ifdef _KERNEL
155     if ((ret = krb5_hmac(context, derived_hmac_key, &d2, &d1)) != 0)
156 	goto cleanup;
157 #else
158     if ((ret = krb5_hmac(context, hash, derived_hmac_key,
159 			1, &d2, &d1)) != 0)
160 	goto cleanup;
161 #endif /* _KERNEL */
162 
163     if (memcmp(cksum, input->data+enclen, hmacsize) != 0) {
164 	ret = KRB5KRB_AP_ERR_BAD_INTEGRITY;
165 	goto cleanup;
166     }
167 
168     /* because this encoding isn't self-describing wrt length, the
169        best we can do here is to compute the length minus the
170        confounder. */
171 
172     plainlen = enclen - blocksize;
173 
174     if (output->length < plainlen) {
175 	ret = KRB5_BAD_MSIZE;
176 	goto cleanup;
177     }
178 
179     output->length = plainlen;
180 
181     (void) memcpy(output->data, d2.data+blocksize, output->length);
182 
183     /*
184      * AES crypto updates the ivec differently, it is handled
185      * in the AES crypto routines directly.
186      */
187     if (cn != NULL &&
188 	key->enctype != ENCTYPE_AES128_CTS_HMAC_SHA1_96 &&
189 	key->enctype != ENCTYPE_AES256_CTS_HMAC_SHA1_96) {
190 	(void) memcpy(ivec->data, cn, blocksize);
191     }
192 
193     ret = 0;
194 
195 cleanup:
196     if (plaindata) {
197 	    (void) memset(plaindata, 0, enclen);
198 	    FREE(plaindata, enclen);
199     }
200     if (cksum) {
201 	    (void) memset(cksum, 0, hashsize);
202 	    FREE(cksum, hashsize);
203     }
204 
205     KRB5_LOG(KRB5_INFO, "krb5_dk_decrypt() end, ret=%d\n", ret);
206     return(ret);
207 }
208 
209