1 files changed, 360 insertions, 0 deletions
diff --git a/src/auths/cram_md5.c b/src/auths/cram_md5.c
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+++ b/src/auths/cram_md5.c
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+/*************************************************
+*     Exim - an Internet mail transport agent    *
+*************************************************/
+
+/* Copyright (c) University of Cambridge 1995 - 2018 */
+/* Copyright (c) The Exim Maintainers 2020 */
+/* See the file NOTICE for conditions of use and distribution. */
+
+
+/* The stand-alone version just tests the algorithm. We have to drag
+in the MD5 computation functions, without their own stand-alone main
+program. */
+
+#ifdef STAND_ALONE
+#define CRAM_STAND_ALONE
+#include "md5.c"
+
+
+/* This is the normal, non-stand-alone case */
+
+#else
+#include "../exim.h"
+#include "cram_md5.h"
+
+/* Options specific to the cram_md5 authentication mechanism. */
+
+optionlist auth_cram_md5_options[] = {
+  { "client_name",        opt_stringptr,
+      OPT_OFF(auth_cram_md5_options_block, client_name) },
+  { "client_secret",      opt_stringptr,
+      OPT_OFF(auth_cram_md5_options_block, client_secret) },
+  { "server_secret",      opt_stringptr,
+      OPT_OFF(auth_cram_md5_options_block, server_secret) }
+};
+
+/* Size of the options list. An extern variable has to be used so that its
+address can appear in the tables drtables.c. */
+
+int auth_cram_md5_options_count =
+  sizeof(auth_cram_md5_options)/sizeof(optionlist);
+
+/* Default private options block for the condition authentication method. */
+
+auth_cram_md5_options_block auth_cram_md5_option_defaults = {
+  NULL,             /* server_secret */
+  NULL,             /* client_secret */
+  NULL              /* client_name */
+};
+
+
+#ifdef MACRO_PREDEF
+
+/* Dummy values */
+void auth_cram_md5_init(auth_instance *ablock) {}
+int auth_cram_md5_server(auth_instance *ablock, uschar *data) {return 0;}
+int auth_cram_md5_client(auth_instance *ablock, void *sx, int timeout,
+    uschar *buffer, int buffsize) {return 0;}
+
+#else	/*!MACRO_PREDEF*/
+
+
+/*************************************************
+*          Initialization entry point            *
+*************************************************/
+
+/* Called for each instance, after its options have been read, to
+enable consistency checks to be done, or anything else that needs
+to be set up. */
+
+void
+auth_cram_md5_init(auth_instance *ablock)
+{
+auth_cram_md5_options_block *ob =
+  (auth_cram_md5_options_block *)(ablock->options_block);
+if (ob->server_secret != NULL) ablock->server = TRUE;
+if (ob->client_secret != NULL)
+  {
+  ablock->client = TRUE;
+  if (ob->client_name == NULL) ob->client_name = primary_hostname;
+  }
+}
+
+#endif	/*!MACRO_PREDEF*/
+#endif  /* STAND_ALONE */
+
+
+
+#ifndef MACRO_PREDEF
+/*************************************************
+*      Perform the CRAM-MD5 algorithm            *
+*************************************************/
+
+/* The CRAM-MD5 algorithm is described in RFC 2195. It computes
+
+  MD5((secret XOR opad), MD5((secret XOR ipad), challenge))
+
+where secret is padded out to 64 characters (after being reduced to an MD5
+digest if longer than 64) and ipad and opad are 64-byte strings of 0x36 and
+0x5c respectively, and comma means concatenation.
+
+Arguments:
+  secret         the shared secret
+  challenge      the challenge text
+  digest         16-byte slot to put the answer in
+
+Returns:         nothing
+*/
+
+static void
+compute_cram_md5(uschar *secret, uschar *challenge, uschar *digestptr)
+{
+md5 base;
+int len = Ustrlen(secret);
+uschar isecret[64];
+uschar osecret[64];
+uschar md5secret[16];
+
+/* If the secret is longer than 64 characters, we compute its MD5 digest
+and use that. */
+
+if (len > 64)
+  {
+  md5_start(&base);
+  md5_end(&base, US secret, len, md5secret);
+  secret = US md5secret;
+  len = 16;
+  }
+
+/* The key length is now known to be <= 64. Set up the padded and xor'ed
+versions. */
+
+memcpy(isecret, secret, len);
+memset(isecret+len, 0, 64-len);
+memcpy(osecret, isecret, 64);
+
+for (int i = 0; i < 64; i++)
+  {
+  isecret[i] ^= 0x36;
+  osecret[i] ^= 0x5c;
+  }
+
+/* Compute the inner MD5 digest */
+
+md5_start(&base);
+md5_mid(&base, isecret);
+md5_end(&base, US challenge, Ustrlen(challenge), md5secret);
+
+/* Compute the outer MD5 digest */
+
+md5_start(&base);
+md5_mid(&base, osecret);
+md5_end(&base, md5secret, 16, digestptr);
+}
+
+
+#ifndef STAND_ALONE
+
+/*************************************************
+*             Server entry point                 *
+*************************************************/
+
+/* For interface, see auths/README */
+
+int
+auth_cram_md5_server(auth_instance *ablock, uschar *data)
+{
+auth_cram_md5_options_block *ob =
+  (auth_cram_md5_options_block *)(ablock->options_block);
+uschar *challenge = string_sprintf("<%d.%ld@%s>", getpid(),
+    (long int) time(NULL), primary_hostname);
+uschar *clear, *secret;
+uschar digest[16];
+int i, rc, len;
+
+/* If we are running in the test harness, always send the same challenge,
+an example string taken from the RFC. */
+
+if (f.running_in_test_harness)
+  challenge = US"<1896.697170952@postoffice.reston.mci.net>";
+
+/* No data should have been sent with the AUTH command */
+
+if (*data) return UNEXPECTED;
+
+/* Send the challenge, read the return */
+
+if ((rc = auth_get_data(&data, challenge, Ustrlen(challenge))) != OK) return rc;
+if ((len = b64decode(data, &clear)) < 0) return BAD64;
+
+/* The return consists of a user name, space-separated from the CRAM-MD5
+digest, expressed in hex. Extract the user name and put it in $auth1 and $1.
+The former is now the preferred variable; the latter is the original one. Then
+check that the remaining length is 32. */
+
+auth_vars[0] = expand_nstring[1] = clear;
+while (*clear && !isspace(*clear)) clear++;
+if (!isspace(*clear)) return FAIL;
+*clear++ = 0;
+
+expand_nlength[1] = clear - expand_nstring[1] - 1;
+if (len - expand_nlength[1] - 1 != 32) return FAIL;
+expand_nmax = 1;
+
+/* Expand the server_secret string so that it can compute a value dependent on
+the user name if necessary. */
+
+debug_print_string(ablock->server_debug_string);    /* customized debugging */
+secret = expand_string(ob->server_secret);
+
+/* A forced fail implies failure of authentication - i.e. we have no secret for
+the given name. */
+
+if (secret == NULL)
+  {
+  if (f.expand_string_forcedfail) return FAIL;
+  auth_defer_msg = expand_string_message;
+  return DEFER;
+  }
+
+/* Compute the CRAM-MD5 digest that we should have received from the client. */
+
+compute_cram_md5(secret, challenge, digest);
+
+HDEBUG(D_auth)
+  {
+  uschar buff[64];
+  debug_printf("CRAM-MD5: user name = %s\n", auth_vars[0]);
+  debug_printf("          challenge = %s\n", challenge);
+  debug_printf("          received  = %s\n", clear);
+  Ustrcpy(buff, US"          digest    = ");
+  for (i = 0; i < 16; i++) sprintf(CS buff+22+2*i, "%02x", digest[i]);
+  debug_printf("%.54s\n", buff);
+  }
+
+/* We now have to compare the digest, which is 16 bytes in binary, with the
+data received, which is expressed in lower case hex. We checked above that
+there were 32 characters of data left. */
+
+for (i = 0; i < 16; i++)
+  {
+  int a = *clear++;
+  int b = *clear++;
+  if (((((a >= 'a')? a - 'a' + 10 : a - '0') << 4) +
+        ((b >= 'a')? b - 'a' + 10 : b - '0')) != digest[i]) return FAIL;
+  }
+
+/* Expand server_condition as an authorization check */
+return auth_check_serv_cond(ablock);
+}
+
+
+
+/*************************************************
+*              Client entry point                *
+*************************************************/
+
+/* For interface, see auths/README */
+
+int
+auth_cram_md5_client(
+  auth_instance *ablock,                 /* authenticator block */
+  void * sx,				 /* smtp connextion */
+  int timeout,                           /* command timeout */
+  uschar *buffer,                        /* for reading response */
+  int buffsize)                          /* size of buffer */
+{
+auth_cram_md5_options_block *ob =
+  (auth_cram_md5_options_block *)(ablock->options_block);
+uschar *secret = expand_string(ob->client_secret);
+uschar *name = expand_string(ob->client_name);
+uschar *challenge, *p;
+int i;
+uschar digest[16];
+
+/* If expansion of either the secret or the user name failed, return CANCELLED
+or ERROR, as appropriate. */
+
+if (!secret || !name)
+  {
+  if (f.expand_string_forcedfail)
+    {
+    *buffer = 0;           /* No message */
+    return CANCELLED;
+    }
+  string_format(buffer, buffsize, "expansion of \"%s\" failed in "
+    "%s authenticator: %s",
+    !secret ? ob->client_secret : ob->client_name,
+    ablock->name, expand_string_message);
+  return ERROR;
+  }
+
+/* Initiate the authentication exchange and read the challenge, which arrives
+in base 64. */
+
+if (smtp_write_command(sx, SCMD_FLUSH, "AUTH %s\r\n", ablock->public_name) < 0)
+  return FAIL_SEND;
+if (!smtp_read_response(sx, buffer, buffsize, '3', timeout))
+  return FAIL;
+
+if (b64decode(buffer + 4, &challenge) < 0)
+  {
+  string_format(buffer, buffsize, "bad base 64 string in challenge: %s",
+    big_buffer + 4);
+  return ERROR;
+  }
+
+/* Run the CRAM-MD5 algorithm on the secret and the challenge */
+
+compute_cram_md5(secret, challenge, digest);
+
+/* Create the response from the user name plus the CRAM-MD5 digest */
+
+string_format(big_buffer, big_buffer_size - 36, "%s", name);
+for (p = big_buffer; *p; ) p++;
+*p++ = ' ';
+
+for (i = 0; i < 16; i++)
+  p += sprintf(CS p, "%02x", digest[i]);
+
+/* Send the response, in base 64, and check the result. The response is
+in big_buffer, but b64encode() returns its result in working store,
+so calling smtp_write_command(), which uses big_buffer, is OK. */
+
+buffer[0] = 0;
+if (smtp_write_command(sx, SCMD_FLUSH, "%s\r\n", b64encode(CUS big_buffer,
+  p - big_buffer)) < 0) return FAIL_SEND;
+
+return smtp_read_response(sx, US buffer, buffsize, '2', timeout)
+  ? OK : FAIL;
+}
+#endif  /* STAND_ALONE */
+
+
+/*************************************************
+**************************************************
+*             Stand-alone test program           *
+**************************************************
+*************************************************/
+
+#ifdef STAND_ALONE
+
+int main(int argc, char **argv)
+{
+int i;
+uschar *secret = US argv[1];
+uschar *challenge = US argv[2];
+uschar digest[16];
+
+compute_cram_md5(secret, challenge, digest);
+
+for (i = 0; i < 16; i++) printf("%02x", digest[i]);
+printf("\n");
+
+return 0;
+}
+
+#endif
+
+#endif	/*!MACRO_PREDEF*/
+/* End of cram_md5.c */