diff --git a/appl/popper/pop_init.c b/appl/popper/pop_init.c
index 3a6ac4693..3fee9c55d 100644
--- a/appl/popper/pop_init.c
+++ b/appl/popper/pop_init.c
@@ -7,22 +7,37 @@
 #include <popper.h>
 RCSID("$Id$");
 
-static
-int
-krb_authenticate(POP *p, struct sockaddr_in *addr)
+#ifdef KRB4
+static int
+krb4_authenticate (POP *p, int s, u_char *buf, struct sockaddr_in *addr)
 {
-
-#ifdef KERBEROS
     Key_schedule schedule;
     KTEXT_ST ticket;
     char instance[INST_SZ];  
     char version[9];
     int auth;
+    u_char buf2[BUFSIZ];
   
+    if (memcmp (buf, KRB_SENDAUTH_VERS, 4) != 0)
+	return -1;
+    if (krb5_net_read (p->context, s, buf + 4,
+		       KRB_SENDAUTH_VLEN - 4) != KRB_SENDAUTH_VLEN - 4)
+	return -1;
+    if (memcmp (buf, KRB_SENDAUTH_VERS, KRB_SENDAUTH_VLEN) != 0)
+	return -1;
+
     k_getsockinst (0, instance, sizeof(instance));
-    auth = krb_recvauth(0L, 0, &ticket, "pop", instance,
-                        addr, (struct sockaddr_in *) NULL,
-                        &p->kdata, "", schedule, version);
+    auth = krb_recvauth(KOPT_IGNORE_PROTOCOL,
+			s,
+			&ticket,
+			"pop",
+			instance,
+                        addr,
+			(struct sockaddr_in *) NULL,
+                        &p->kdata,
+			"",
+			schedule,
+			version);
     
     if (auth != KSUCCESS) {
         pop_msg(p, POP_FAILURE, "Kerberos authentication failure: %s", 
@@ -37,14 +52,86 @@ krb_authenticate(POP *p, struct sockaddr_in *addr)
     pop_log(p, POP_DEBUG, "%s.%s@%s (%s): ok", p->kdata.pname, 
             p->kdata.pinst, p->kdata.prealm, inet_ntoa(addr->sin_addr));
 #endif /* DEBUG */
+    return 0;
+}
+#endif /* KRB4 */
 
+static int
+krb5_authenticate (POP *p, int s, u_char *buf, struct sockaddr_in *addr)
+{
+    krb5_error_code ret;
+    krb5_auth_context auth_context = NULL;
+    u_int32_t len;
+    krb5_principal server;
+    krb5_ticket *ticket;
+
+    if (memcmp (buf, "\x00\x00\x00\x13", 4) != 0)
+	return -1;
+    len = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | (buf[3]);
+	
+    if (krb5_net_read(p->context, s, buf, len) != len)
+	return -1;
+    if (len != sizeof(KRB5_SENDAUTH_VERSION)
+	|| memcmp (buf, KRB5_SENDAUTH_VERSION, len) != 0)
+	return -1;
+    
+    ret = krb5_sname_to_principal (p->context,
+				   p->myhost,
+				   "pop",
+				   KRB5_NT_SRV_HST,
+				   &server);
+    if (ret) {
+	pop_log (p, POP_FAILURE,
+		 "krb5_sname_to_principal: %s",
+		 krb5_get_err_text(p->context, ret));
+	exit (1);
+    }
+
+    ret = krb5_recvauth (p->context,
+			 &auth_context,
+			 &s,
+			 "KPOPV1.0",
+			 server,
+			 KRB5_RECVAUTH_IGNORE_VERSION,
+			 NULL,
+			 &ticket);
+    krb5_free_principal (p->context, server);
+    if (ret == 0) {
+	krb5_auth_con_free (p->context, auth_context);
+	krb5_copy_principal (p->context, ticket->client, &p->principal);
+	krb5_free_ticket (p->context, ticket);
+    }
+    return ret;
+}
+
+static int
+krb_authenticate(POP *p, struct sockaddr_in *addr)
+{
+#ifdef KERBEROS
+    u_char buf[BUFSIZ];
+
+    if (krb5_net_read (p->context, 0, buf, 4) != 4) {
+	pop_msg(p, POP_FAILURE, "Reading four bytes: %s",
+		strerror(errno));
+	exit (1);
+    }
+#ifdef KRB4
+    if (krb4_authenticate (p, 0, buf, addr) == 0)
+	p->version = 4;
+    else
+#endif /* KRB4 */
+    if (krb5_authenticate (p, 0, buf, addr) == 0)
+	p->version = 5;
+    else {
+	exit (1);
+    }
+	
 #endif /* KERBEROS */
 
     return(POP_SUCCESS);
 }
 
-static
-int
+static int
 plain_authenticate (POP *p, struct sockaddr_in *addr)
 {
     return(POP_SUCCESS);
@@ -75,7 +162,7 @@ pop_init(POP *p,int argcount,char **argmessage)
     p->myname = argmessage[0];
 
     /*  Get the name of our host */
-    k_gethostname(p->myhost,MaxHostNameLen);
+    gethostname(p->myhost,MaxHostNameLen);
 
     /*  Open the log file */
     openlog(p->myname,POP_LOGOPTS,POP_FACILITY);
@@ -153,8 +240,8 @@ pop_init(POP *p,int argcount,char **argmessage)
     if (inetd) {
 	if (portnum == 0)
 	    portnum = p->kerberosp ?
-		k_getportbyname("kpop", "tcp", htons(1109)) :
-	    k_getportbyname("pop", "tcp", htons(110));
+		krb5_getportbyname("kpop", "tcp", htons(1109)) :
+	    krb5_getportbyname("pop", "tcp", htons(110));
 	mini_inetd (portnum);
     }
 
@@ -245,5 +332,9 @@ pop_init(POP *p,int argcount,char **argmessage)
         pop_log(p,POP_PRIORITY,"Debugging turned on");
 #endif /* DEBUG */
 
+#ifdef KERBEROS
+    krb5_init_context (&p->context);
+#endif
+
     return((p->kerberosp ? krb_authenticate : plain_authenticate)(p, &cs));
 }
diff --git a/appl/popper/pop_pass.c b/appl/popper/pop_pass.c
index 71e8c44e3..d81c5d92e 100644
--- a/appl/popper/pop_pass.c
+++ b/appl/popper/pop_pass.c
@@ -7,6 +7,95 @@
 #include <popper.h>
 RCSID("$Id$");
 
+#ifdef KRB4
+static int
+krb4_verify_password (POP *p)
+{
+    int status;
+    char lrealm[REALM_SZ + 1];
+    char tkt[MaxPathLen];
+
+    status = krb_get_lrealm(lrealm,1);
+    if (status == KFAILURE) {
+        pop_log(p, POP_FAILURE, "%s: (%s.%s@%s) %s", p->client,
+		p->kdata.pname, p->kdata.pinst, p->kdata.prealm,
+		krb_get_err_text(status));
+	return 1;
+    }
+    snprintf (tkt, sizeof(tkt),
+	      TKT_ROOT "_popper.%u", (unsigned)getpid());
+    krb_set_tkt_string (tkt);
+
+    return krb_verify_user(p->user, "", lrealm, p->pop_parm[1],
+			   1, "pop");
+}
+#endif /* KRB4 */
+
+static int
+krb5_verify_password (POP *p)
+{
+    krb5_preauthtype pre_auth_types[] = {KRB5_PADATA_ENC_TIMESTAMP};
+    krb5_get_init_creds_opt get_options;
+    krb5_verify_init_creds_opt verify_options;
+    krb5_error_code ret;
+    krb5_principal client, server;
+    krb5_creds creds;
+
+    krb5_get_init_creds_opt_init (&get_options);
+
+    krb5_get_init_creds_opt_set_preauth_list (&get_options,
+					      pre_auth_types,
+					      1);
+
+    krb5_verify_init_creds_opt_init (&verify_options);
+    
+    ret = krb5_parse_name (p->context, p->user, &client);
+    if (ret) {
+	pop_log(p, POP_FAILURE, "krb5_parse_name: %s",
+		krb5_get_err_text (p->context, ret));
+	return 1;
+    }
+
+    ret = krb5_get_init_creds_password (p->context,
+					&creds,
+					client,
+					p->pop_parm[1],
+					NULL,
+					NULL,
+					0,
+					NULL,
+					&get_options);
+    if (ret) {
+	pop_log(p, POP_FAILURE,
+		"krb5_get_init_creds_password: %s",
+		krb5_get_err_text (p->context, ret));
+	return 1;
+    }
+
+    ret = krb5_sname_to_principal (p->context,
+				   p->myhost,
+				   "pop",
+				   KRB5_NT_SRV_HST,
+				   &server);
+    if (ret) {
+	pop_log(p, POP_FAILURE,
+		"krb5_get_init_creds_password: %s",
+		krb5_get_err_text (p->context, ret));
+	return 1;
+    }
+
+    ret = krb5_verify_init_creds (p->context,
+				  &creds,
+				  server,
+				  NULL,
+				  NULL,
+				  &verify_options);
+    krb5_free_principal (p->context, client);
+    krb5_free_principal (p->context, server);
+    krb5_free_creds_contents (p->context, &creds);
+    return ret;
+}
+
 /* 
  *  pass:   Obtain the user password from a POP client
  */
@@ -15,8 +104,6 @@ int
 pop_pass (POP *p)
 {
     struct passwd  *pw;
-    char lrealm[REALM_SZ + 1];
-    int status; 
     int i;
 
     /* Make one string of all these parameters */
@@ -30,18 +117,32 @@ pop_pass (POP *p)
 			"Password supplied for \"%s\" is incorrect.",
 			p->user));
 
-    if ((status = krb_get_lrealm(lrealm,1)) == KFAILURE) {
-        pop_log(p, POP_FAILURE, "%s: (%s.%s@%s) %s", p->client,
-		p->kdata.pname, p->kdata.pinst, p->kdata.prealm,
-		krb_get_err_text(status));
-        return(pop_msg(p,POP_FAILURE,
-		       "Kerberos error:  \"%s\".",
-		       krb_get_err_text(status)));
-    }
-
-    if (!p->kerberosp) {
-	 char tkt[MaxPathLen];
-
+    if (p->kerberosp) {
+#ifdef KRB4
+	if (p->version == 4) {
+	    if(kuserok (&p->kdata, p->user)) {
+		pop_log(p, POP_FAILURE,
+			"%s: (%s.%s@%s) tried to retrieve mail for %s.",
+			p->client, p->kdata.pname, p->kdata.pinst,
+			p->kdata.prealm, p->user);
+		return(pop_msg(p,POP_FAILURE,
+			       "Popping not authorized"));
+	    }
+	} else
+#endif /* KRB4 */
+	    if (p->version == 5) {
+		if (!krb5_kuserok (p->context, p->principal, p->user)) {
+		    pop_log (p, POP_FAILURE,
+			     "krb5 permission denied");
+		    return pop_msg(p, POP_FAILURE,
+				   "Popping not authorized");
+		}
+	    } else {
+		pop_log (p, POP_FAILURE, "kerberos authentication failed");
+		return pop_msg (p, POP_FAILURE,
+				"kerberos authentication failed");
+	    }
+    } else {
 	 /*  We don't accept connections from users with null passwords */
 	 if (pw->pw_passwd == NULL)
 	      return (pop_msg(p,
@@ -49,32 +150,23 @@ pop_pass (POP *p)
 			      "Password supplied for \"%s\" is incorrect.",
 			      p->user));
 
-	 snprintf (tkt, sizeof(tkt),
-		   TKT_ROOT "_popper.%u", (unsigned)getpid());
-	 krb_set_tkt_string (tkt);
 	 if (otp_verify_user (&p->otp_ctx, p->pop_parm[1]) == 0)
 	     ;
 	 else if(p->auth_level != AUTH_NONE)
 	     return pop_msg(p, POP_FAILURE,
 			    "Password supplied for \"%s\" is incorrect.",
 			    p->user);
-	 else if (krb_verify_user(p->user, "", lrealm, p->pop_parm[1],
-				  1, "pop") &&
-		  unix_verify_user(p->user, p->pop_parm[1])) {
-	     dest_tkt ();
-	     return (pop_msg(p,POP_FAILURE,
-			     "Password supplied for \"%s\" is incorrect.",
-			     p->user));
-	 }
-	 dest_tkt ();
-    } else {
-	 if (kuserok (&p->kdata, p->user)) {
-	      pop_log(p, POP_FAILURE,
-		      "%s: (%s.%s@%s) tried to retrieve mail for %s.",
-		      p->client, p->kdata.pname, p->kdata.pinst,
-		      p->kdata.prealm, p->user);
-	      return(pop_msg(p,POP_FAILURE,
-			     "Popping not authorized"));
+	 else {
+#ifdef KRB4
+	     if (krb4_verify_password (p) == 0)
+		 ;
+	     else
+#endif /* KRB4 */
+		 if (krb5_verify_password (p) == 0)
+		     ;
+	     else
+		 return pop_msg(p, POP_FAILURE,
+				"Password incorrect");
 	 }
     }