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/* Copyright (C) 2014 mod_auth_gssapi authors - See COPYING for (C) terms */
#include <openssl/evp.h>
#include <openssl/hmac.h>
#include <openssl/rand.h>
#include <stdbool.h>
#include "crypto.h"
struct seal_key {
const EVP_CIPHER *cipher;
const EVP_MD *md;
unsigned char *ekey;
unsigned char *hkey;
};
apr_status_t SEAL_KEY_CREATE(apr_pool_t *p, struct seal_key **skey,
struct databuf *keys)
{
struct seal_key *n;
int keylen;
int ret;
n = apr_pcalloc(p, sizeof(*n));
if (!n) return ENOMEM;
n->cipher = EVP_aes_128_cbc();
if (!n->cipher) {
ret = EFAULT;
goto done;
}
keylen = n->cipher->key_len;
n->md = EVP_sha256();
if (!n->md) {
ret = EFAULT;
goto done;
}
n->ekey = apr_palloc(p, keylen);
if (!n->ekey) {
ret = ENOMEM;
goto done;
}
n->hkey = apr_palloc(p, keylen);
if (!n->hkey) {
ret = ENOMEM;
goto done;
}
if (keys) {
if (keys->length != (keylen * 2)) {
ret = EINVAL;
goto done;
}
memcpy(n->ekey, keys->value, keylen);
memcpy(n->hkey, keys->value + keylen, keylen);
} else {
ret = RAND_bytes(n->ekey, keylen);
if (ret == 0) {
ret = EFAULT;
goto done;
}
ret = RAND_bytes(n->hkey, keylen);
if (ret == 0) {
ret = EFAULT;
goto done;
}
}
ret = 0;
done:
if (ret) {
free(n->ekey);
free(n->hkey);
free(n);
} else {
*skey = n;
}
return ret;
}
apr_status_t SEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
struct databuf *plain, struct databuf *cipher)
{
apr_status_t err = EFAULT;
EVP_CIPHER_CTX ctx = { 0 };
HMAC_CTX hmac_ctx = { 0 };
uint8_t rbuf[16];
unsigned int len;
int outlen, totlen;
int ret;
EVP_CIPHER_CTX_init(&ctx);
/* confounder to avoid exposing random numbers directly to clients
* as IVs */
ret = RAND_bytes(rbuf, 16);
if (ret == 0) goto done;
if (cipher->length == 0) {
/* add space for confounder and padding and MAC */
cipher->length = (plain->length / 16 + 2) * 16;
cipher->value = apr_palloc(p, cipher->length + skey->md->md_size);
if (!cipher->value) {
err = ENOMEM;
goto done;
}
}
ret = EVP_EncryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
if (ret == 0) goto done;
totlen = 0;
outlen = cipher->length;
ret = EVP_EncryptUpdate(&ctx, cipher->value, &outlen, rbuf, 16);
if (ret == 0) goto done;
totlen += outlen;
outlen = cipher->length - totlen;
ret = EVP_EncryptUpdate(&ctx, &cipher->value[totlen], &outlen,
plain->value, plain->length);
if (ret == 0) goto done;
totlen += outlen;
outlen = cipher->length - totlen;
ret = EVP_EncryptFinal_ex(&ctx, &cipher->value[totlen], &outlen);
if (ret == 0) goto done;
totlen += outlen;
/* now MAC the buffer */
HMAC_CTX_init(&hmac_ctx);
ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
skey->cipher->key_len, skey->md, NULL);
if (ret == 0) goto done;
ret = HMAC_Update(&hmac_ctx, cipher->value, totlen);
if (ret == 0) goto done;
ret = HMAC_Final(&hmac_ctx, &cipher->value[totlen], &len);
if (ret == 0) goto done;
cipher->length = totlen + len;
err = 0;
done:
EVP_CIPHER_CTX_cleanup(&ctx);
HMAC_CTX_cleanup(&hmac_ctx);
return err;
}
apr_status_t UNSEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
struct databuf *cipher, struct databuf *plain)
{
apr_status_t err = EFAULT;
EVP_CIPHER_CTX ctx = { 0 };
HMAC_CTX hmac_ctx = { 0 };
unsigned char mac[skey->md->md_size];
unsigned int len;
int outlen, totlen;
volatile bool equal = true;
int ret, i;
/* check MAC first */
HMAC_CTX_init(&hmac_ctx);
ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
skey->cipher->key_len, skey->md, NULL);
if (ret == 0) goto done;
cipher->length -= skey->md->md_size;
ret = HMAC_Update(&hmac_ctx, cipher->value, cipher->length);
if (ret == 0) goto done;
ret = HMAC_Final(&hmac_ctx, mac, &len);
if (ret == 0) goto done;
if (len != skey->md->md_size) goto done;
for (i = 0; i < skey->md->md_size; i++) {
if (cipher->value[cipher->length + i] != mac[i]) equal = false;
/* not breaking intentionally,
* or we would allow an oracle attack */
}
if (!equal) goto done;
EVP_CIPHER_CTX_init(&ctx);
if (plain->length == 0) {
plain->length = cipher->length;
plain->value = apr_palloc(p, plain->length);
if (!plain->value) {
err = ENOMEM;
goto done;
}
}
ret = EVP_DecryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
if (ret == 0) goto done;
totlen = 0;
outlen = plain->length;
ret = EVP_DecryptUpdate(&ctx, plain->value, &outlen,
cipher->value, cipher->length);
if (ret == 0) goto done;
totlen += outlen;
outlen = plain->length - totlen;
ret = EVP_DecryptFinal_ex(&ctx, plain->value, &outlen);
if (ret == 0) goto done;
totlen += outlen;
/* now remove the confounder */
totlen -= 16;
memmove(plain->value, plain->value + 16, totlen);
plain->length = totlen;
err = 0;
done:
EVP_CIPHER_CTX_cleanup(&ctx);
HMAC_CTX_cleanup(&hmac_ctx);
return err;
}
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