1 /*-
2 * Copyright 2022-2023 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9 #include <string.h>
10 #include <openssl/decoder.h>
11 #include <openssl/encoder.h>
12 #include <openssl/evp.h>
13
14 /*
15 * Example showing the encoding and decoding of RSA public and private keys. A
16 * PEM-encoded RSA key is read in from stdin, decoded, and then re-encoded and
17 * output for demonstration purposes. Both public and private keys are accepted.
18 *
19 * This can be used to load RSA keys from a file or save RSA keys to a file.
20 */
21
22 /* A property query used for selecting algorithm implementations. */
23 static const char *propq = NULL;
24
25 /*
26 * Load a PEM-encoded RSA key from a file, optionally decrypting it with a
27 * supplied passphrase.
28 */
load_key(OSSL_LIB_CTX * libctx,FILE * f,const char * passphrase)29 static EVP_PKEY *load_key(OSSL_LIB_CTX *libctx, FILE *f, const char *passphrase)
30 {
31 int ret = 0;
32 EVP_PKEY *pkey = NULL;
33 OSSL_DECODER_CTX *dctx = NULL;
34 int selection = 0;
35
36 /*
37 * Create PEM decoder context expecting an RSA key.
38 *
39 * For raw (non-PEM-encoded) keys, change "PEM" to "DER".
40 *
41 * The selection argument here specifies whether we are willing to accept a
42 * public key, private key, or either. If it is set to zero, either will be
43 * accepted. If set to EVP_PKEY_KEYPAIR, a private key will be required, and
44 * if set to EVP_PKEY_PUBLIC_KEY, a public key will be required.
45 */
46 dctx = OSSL_DECODER_CTX_new_for_pkey(&pkey, "PEM", NULL, "RSA",
47 selection,
48 libctx, propq);
49 if (dctx == NULL) {
50 fprintf(stderr, "OSSL_DECODER_CTX_new_for_pkey() failed\n");
51 goto cleanup;
52 }
53
54 /*
55 * Set passphrase if provided; needed to decrypt encrypted PEM files.
56 * If the input is not encrypted, any passphrase provided is ignored.
57 *
58 * Alternative methods for specifying passphrases exist, such as a callback
59 * (see OSSL_DECODER_CTX_set_passphrase_cb(3)), which may be more useful for
60 * interactive applications which do not know if a passphrase should be
61 * prompted for in advance, or for GUI applications.
62 */
63 if (passphrase != NULL) {
64 if (OSSL_DECODER_CTX_set_passphrase(dctx,
65 (const unsigned char *)passphrase,
66 strlen(passphrase)) == 0) {
67 fprintf(stderr, "OSSL_DECODER_CTX_set_passphrase() failed\n");
68 goto cleanup;
69 }
70 }
71
72 /* Do the decode, reading from file. */
73 if (OSSL_DECODER_from_fp(dctx, f) == 0) {
74 fprintf(stderr, "OSSL_DECODER_from_fp() failed\n");
75 goto cleanup;
76 }
77
78 ret = 1;
79 cleanup:
80 OSSL_DECODER_CTX_free(dctx);
81
82 /*
83 * pkey is created by OSSL_DECODER_CTX_new_for_pkey, but we
84 * might fail subsequently, so ensure it's properly freed
85 * in this case.
86 */
87 if (ret == 0) {
88 EVP_PKEY_free(pkey);
89 pkey = NULL;
90 }
91
92 return pkey;
93 }
94
95 /*
96 * Store an RSA public or private key to a file using PEM encoding.
97 *
98 * If a passphrase is supplied, the file is encrypted, otherwise
99 * it is unencrypted.
100 */
store_key(EVP_PKEY * pkey,FILE * f,const char * passphrase)101 static int store_key(EVP_PKEY *pkey, FILE *f, const char *passphrase)
102 {
103 int ret = 0;
104 int selection;
105 OSSL_ENCODER_CTX *ectx = NULL;
106
107 /*
108 * Create a PEM encoder context.
109 *
110 * For raw (non-PEM-encoded) output, change "PEM" to "DER".
111 *
112 * The selection argument controls whether the private key is exported
113 * (EVP_PKEY_KEYPAIR), or only the public key (EVP_PKEY_PUBLIC_KEY). The
114 * former will fail if we only have a public key.
115 *
116 * Note that unlike the decode API, you cannot specify zero here.
117 *
118 * Purely for the sake of demonstration, here we choose to export the whole
119 * key if a passphrase is provided and the public key otherwise.
120 */
121 selection = (passphrase != NULL)
122 ? EVP_PKEY_KEYPAIR
123 : EVP_PKEY_PUBLIC_KEY;
124
125 ectx = OSSL_ENCODER_CTX_new_for_pkey(pkey, selection, "PEM", NULL, propq);
126 if (ectx == NULL) {
127 fprintf(stderr, "OSSL_ENCODER_CTX_new_for_pkey() failed\n");
128 goto cleanup;
129 }
130
131 /*
132 * Set passphrase if provided; the encoded output will then be encrypted
133 * using the passphrase.
134 *
135 * Alternative methods for specifying passphrases exist, such as a callback
136 * (see OSSL_ENCODER_CTX_set_passphrase_cb(3), just as for OSSL_DECODER_CTX;
137 * however you are less likely to need them as you presumably know whether
138 * encryption is desired in advance.
139 *
140 * Note that specifying a passphrase alone is not enough to cause the
141 * key to be encrypted. You must set both a cipher and a passphrase.
142 */
143 if (passphrase != NULL) {
144 /* Set cipher. AES-128-CBC is a reasonable default. */
145 if (OSSL_ENCODER_CTX_set_cipher(ectx, "AES-128-CBC", propq) == 0) {
146 fprintf(stderr, "OSSL_ENCODER_CTX_set_cipher() failed\n");
147 goto cleanup;
148 }
149
150 /* Set passphrase. */
151 if (OSSL_ENCODER_CTX_set_passphrase(ectx,
152 (const unsigned char *)passphrase,
153 strlen(passphrase)) == 0) {
154 fprintf(stderr, "OSSL_ENCODER_CTX_set_passphrase() failed\n");
155 goto cleanup;
156 }
157 }
158
159 /* Do the encode, writing to the given file. */
160 if (OSSL_ENCODER_to_fp(ectx, f) == 0) {
161 fprintf(stderr, "OSSL_ENCODER_to_fp() failed\n");
162 goto cleanup;
163 }
164
165 ret = 1;
166 cleanup:
167 OSSL_ENCODER_CTX_free(ectx);
168 return ret;
169 }
170
main(int argc,char ** argv)171 int main(int argc, char **argv)
172 {
173 int ret = EXIT_FAILURE;
174 OSSL_LIB_CTX *libctx = NULL;
175 EVP_PKEY *pkey = NULL;
176 const char *passphrase_in = NULL, *passphrase_out = NULL;
177
178 /* usage: rsa_encode <passphrase-in> <passphrase-out> */
179 if (argc > 1 && argv[1][0])
180 passphrase_in = argv[1];
181
182 if (argc > 2 && argv[2][0])
183 passphrase_out = argv[2];
184
185 /* Decode PEM key from stdin and then PEM encode it to stdout. */
186 pkey = load_key(libctx, stdin, passphrase_in);
187 if (pkey == NULL) {
188 fprintf(stderr, "Failed to decode key\n");
189 goto cleanup;
190 }
191
192 if (store_key(pkey, stdout, passphrase_out) == 0) {
193 fprintf(stderr, "Failed to encode key\n");
194 goto cleanup;
195 }
196
197 ret = EXIT_SUCCESS;
198 cleanup:
199 EVP_PKEY_free(pkey);
200 OSSL_LIB_CTX_free(libctx);
201 return ret;
202 }
203
