Refactor confirm_weak to use SeatDialogText.

This centralises the messages for weak crypto algorithms (general, and
host keys in particular, the latter including a list of all the other
available host key types) into ssh/common.c, in much the same way as
we previously did for ordinary host key warnings.

The reason is the same too: I'm about to want to vary the text in one
of those dialog boxes, so it's convenient to start by putting it
somewhere that I can modify just once.

console.c

@@ -9,18 +9,6 @@
 #include "misc.h"
 #include "console.h"
 
-const char weakcrypto_msg_common_fmt[] =
-    "The first %s supported by the server is\n"
-    "%s, which is below the configured warning threshold.\n";
-
-const char weakhk_msg_common_fmt[] =
-    "The first host key type we have stored for this server\n"
-    "is %s, which is below the configured warning threshold.\n"
-    "The server also provides the following types of host key\n"
-    "above the threshold, which we do not have stored:\n"
-    "%s\n";
-
-const char console_continue_prompt[] = "Continue with connection? (y/n) ";
 const char console_abandoned_msg[] = "Connection abandoned.\n";
 
 const SeatDialogPromptDescriptions *console_prompt_descriptions(Seat *seat)
@@ -30,6 +18,8 @@ const SeatDialogPromptDescriptions *console_prompt_descriptions(Seat *seat)
         .hk_connect_once_action = "enter \"n\"",
         .hk_cancel_action = "press Return",
         .hk_cancel_action_Participle = "Pressing Return",
+        .weak_accept_action = "enter \"y\"",
+        .weak_cancel_action = "enter \"n\"",
     };
     return &descs;
 }

proxy/sshproxy.c

@@ -430,8 +430,32 @@ static SeatPromptResult sshproxy_confirm_ssh_host_key(
     return SPR_SW_ABORT("Noninteractive SSH proxy cannot confirm host key");
 }
 
+static void sshproxy_format_seatdialogtext(strbuf *sb, SeatDialogText *text)
+{
+    for (SeatDialogTextItem *item = text->items,
+             *end = item+text->nitems; item < end; item++) {
+        switch (item->type) {
+          case SDT_SCARY_HEADING:
+          case SDT_PARA:
+          case SDT_DISPLAY:
+            put_stringz(sb, item->text);
+            put_byte(sb, '\n');
+            break;
+          case SDT_BATCH_ABORT:
+            put_stringz(sb, item->text);
+            put_byte(sb, '\n');
+            goto endloop;
+          default:
+            break;
+        }
+    }
+
+  endloop:
+    while (strbuf_chomp(sb, '\n'));
+}
+
 static SeatPromptResult sshproxy_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     SshProxy *sp = container_of(seat, SshProxy, seat);
@@ -442,22 +466,24 @@ static SeatPromptResult sshproxy_confirm_weak_crypto_primitive(
          * request on to it.
          */
         return seat_confirm_weak_crypto_primitive(
-            wrap(sp->clientseat), algtype, algname, callback, ctx);
+            wrap(sp->clientseat), text, callback, ctx);
     }
 
     /*
      * Otherwise, behave as if we're in batch mode: take the safest
      * option.
      */
-    sshproxy_error(sp, "First %s supported by server is %s, below warning "
+    strbuf *sb = strbuf_new();
-                   "threshold. Abandoning proxy SSH connection.",
+    sshproxy_format_seatdialogtext(sb, text);
-                   algtype, algname);
+    sshproxy_error(sp, sb->s);
+    strbuf_free(sb);
+
     return SPR_SW_ABORT("Noninteractive SSH proxy cannot confirm "
                         "weak crypto primitive");
 }
 
 static SeatPromptResult sshproxy_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     SshProxy *sp = container_of(seat, SshProxy, seat);
@@ -468,16 +494,18 @@ static SeatPromptResult sshproxy_confirm_weak_cached_hostkey(
          * request on to it.
          */
         return seat_confirm_weak_cached_hostkey(
-            wrap(sp->clientseat), algname, betteralgs, callback, ctx);
+            wrap(sp->clientseat), text, callback, ctx);
     }
 
     /*
      * Otherwise, behave as if we're in batch mode: take the safest
      * option.
      */
-    sshproxy_error(sp, "First host key type stored for server is %s, below "
+    strbuf *sb = strbuf_new();
-                   "warning threshold. Abandoning proxy SSH connection.",
+    sshproxy_format_seatdialogtext(sb, text);
-                   algname);
+    sshproxy_error(sp, sb->s);
+    strbuf_free(sb);
+
     return SPR_SW_ABORT("Noninteractive SSH proxy cannot confirm "
                         "weak cached host key");
 }

putty.h

@@ -1293,7 +1293,7 @@ struct SeatVtable {
      * confirm_ssh_host_key above.
      */
     SeatPromptResult (*confirm_weak_crypto_primitive)(
-        Seat *seat, const char *algtype, const char *algname,
+        Seat *seat, SeatDialogText *text,
         void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 
     /*
@@ -1304,11 +1304,10 @@ struct SeatVtable {
      * This form is used in the case where we're using a host key
      * below the warning threshold because that's the best one we have
      * cached, but at least one host key algorithm *above* the
-     * threshold is available that we don't have cached. 'betteralgs'
+     * threshold is available that we don't have cached.
-     * lists the better algorithm(s).
      */
     SeatPromptResult (*confirm_weak_cached_hostkey)(
-        Seat *seat, const char *algname, const char *betteralgs,
+        Seat *seat, SeatDialogText *text,
         void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 
     /*
@@ -1444,15 +1443,15 @@ static inline SeatPromptResult seat_confirm_ssh_host_key(
 { return iseat.seat->vt->confirm_ssh_host_key(
         iseat.seat, h, p, ktyp, kstr, text, helpctx, cb, ctx); }
 static inline SeatPromptResult seat_confirm_weak_crypto_primitive(
-    InteractionReadySeat iseat, const char *atyp, const char *aname,
+    InteractionReadySeat iseat, SeatDialogText *text,
     void (*cb)(void *ctx, SeatPromptResult result), void *ctx)
 { return iseat.seat->vt->confirm_weak_crypto_primitive(
-        iseat.seat, atyp, aname, cb, ctx); }
+        iseat.seat, text, cb, ctx); }
 static inline SeatPromptResult seat_confirm_weak_cached_hostkey(
-    InteractionReadySeat iseat, const char *aname, const char *better,
+    InteractionReadySeat iseat, SeatDialogText *text,
     void (*cb)(void *ctx, SeatPromptResult result), void *ctx)
 { return iseat.seat->vt->confirm_weak_cached_hostkey(
-        iseat.seat, aname, better, cb, ctx); }
+        iseat.seat, text, cb, ctx); }
 static inline const SeatDialogPromptDescriptions *seat_prompt_descriptions(
     Seat *seat)
 { return seat->vt->prompt_descriptions(seat); }
@@ -1505,6 +1504,7 @@ struct SeatDialogPromptDescriptions {
     const char *hk_accept_action;
     const char *hk_connect_once_action;
     const char *hk_cancel_action, *hk_cancel_action_Participle;
+    const char *weak_accept_action, *weak_cancel_action;
 };
 
 /* In the utils subdir: print a message to the Seat which can't be
@@ -1537,10 +1537,10 @@ SeatPromptResult nullseat_confirm_ssh_host_key(
     char *keystr, SeatDialogText *text, HelpCtx helpctx,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult nullseat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult nullseat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 const SeatDialogPromptDescriptions *nullseat_prompt_descriptions(Seat *seat);
 bool nullseat_is_never_utf8(Seat *seat);
@@ -1573,10 +1573,10 @@ SeatPromptResult console_confirm_ssh_host_key(
     char *keystr, SeatDialogText *text, HelpCtx helpctx,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult console_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult console_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 StripCtrlChars *console_stripctrl_new(
     Seat *seat, BinarySink *bs_out, SeatInteractionContext sic);

ssh.h

@@ -1908,6 +1908,12 @@ SeatPromptResult verify_ssh_host_key(
     ssh_key *key, const char *keytype, char *keystr, const char *keydisp,
     char **fingerprints, int ca_count,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
+SeatPromptResult confirm_weak_crypto_primitive(
+    InteractionReadySeat iseat, const char *algtype, const char *algname,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
+SeatPromptResult confirm_weak_cached_hostkey(
+    InteractionReadySeat iseat, const char *algname, const char **betteralgs,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 
 typedef struct ssh_transient_hostkey_cache ssh_transient_hostkey_cache;
 ssh_transient_hostkey_cache *ssh_transient_hostkey_cache_new(void);

ssh/common.c

@@ -1085,6 +1085,79 @@ SeatPromptResult verify_ssh_host_key(
     return toret;
 }
 
+SeatPromptResult confirm_weak_crypto_primitive(
+    InteractionReadySeat iseat, const char *algtype, const char *algname,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+{
+    SeatDialogText *text = seat_dialog_text_new();
+    const SeatDialogPromptDescriptions *pds =
+        seat_prompt_descriptions(iseat.seat);
+
+    seat_dialog_text_append(text, SDT_TITLE, "%s Security Alert", appname);
+
+    seat_dialog_text_append(
+        text, SDT_PARA,
+        "The first %s supported by the server is %s, "
+        "which is below the configured warning threshold.",
+        algtype, algname);
+
+    /* In batch mode, we print the above information and then this
+     * abort message, and stop. */
+    seat_dialog_text_append(text, SDT_BATCH_ABORT, "Connection abandoned.");
+
+    seat_dialog_text_append(
+        text, SDT_PARA, "To accept the risk and continue, %s. "
+        "To abandon the connection, %s.",
+        pds->weak_accept_action, pds->weak_cancel_action);
+
+    seat_dialog_text_append(text, SDT_PROMPT, "Continue with connection?");
+
+    SeatPromptResult toret = seat_confirm_weak_crypto_primitive(
+        iseat, text, callback, ctx);
+    seat_dialog_text_free(text);
+    return toret;
+}
+
+SeatPromptResult confirm_weak_cached_hostkey(
+    InteractionReadySeat iseat, const char *algname, const char **betteralgs,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+{
+    SeatDialogText *text = seat_dialog_text_new();
+    const SeatDialogPromptDescriptions *pds =
+        seat_prompt_descriptions(iseat.seat);
+
+    seat_dialog_text_append(text, SDT_TITLE, "%s Security Alert", appname);
+
+    seat_dialog_text_append(
+        text, SDT_PARA,
+        "The first host key type we have stored for this server "
+        "is %s, which is below the configured warning threshold.", algname);
+
+    seat_dialog_text_append(
+        text, SDT_PARA,
+        "The server also provides the following types of host key "
+        "above the threshold, which we do not have stored:");
+
+    for (const char **p = betteralgs; *p; p++)
+        seat_dialog_text_append(text, SDT_DISPLAY, "%s", *p);
+
+    /* In batch mode, we print the above information and then this
+     * abort message, and stop. */
+    seat_dialog_text_append(text, SDT_BATCH_ABORT, "Connection abandoned.");
+
+    seat_dialog_text_append(
+        text, SDT_PARA, "To accept the risk and continue, %s. "
+        "To abandon the connection, %s.",
+        pds->weak_accept_action, pds->weak_cancel_action);
+
+    seat_dialog_text_append(text, SDT_PROMPT, "Continue with connection?");
+
+    SeatPromptResult toret = seat_confirm_weak_cached_hostkey(
+        iseat, text, callback, ctx);
+    seat_dialog_text_free(text);
+    return toret;
+}
+
 /* ----------------------------------------------------------------------
  * Common functions shared between SSH-1 layers.
  */

ssh/login1.c

@@ -323,7 +323,7 @@ static void ssh1_login_process_queue(PacketProtocolLayer *ppl)
 
         /* Warn about chosen cipher if necessary. */
         if (warn) {
-            s->spr = seat_confirm_weak_crypto_primitive(
+            s->spr = confirm_weak_crypto_primitive(
                 ppl_get_iseat(&s->ppl), "cipher", cipher_string,
                 ssh1_login_dialog_callback, s);
             crMaybeWaitUntilV(s->spr.kind != SPRK_INCOMPLETE);

ssh/server.c

@@ -98,11 +98,11 @@ void mainchan_terminal_size(mainchan *mc, int width, int height) {}
 /* Seat functions to ensure we don't get choosy about crypto - as the
  * server, it's not up to us to give user warnings */
 static SeatPromptResult server_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 { return SPR_OK; }
 static SeatPromptResult server_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 { return SPR_OK; }
 

ssh/transport2.c

@@ -1514,7 +1514,8 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
 
     if (s->warn_hk) {
         int j, k;
-        char *betteralgs;
+        const char **betteralgs = NULL;
+        size_t nbetter = 0, bettersize = 0;
 
         /*
          * Change warning box wording depending on why we chose a
@@ -1523,7 +1524,6 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
          * could usefully cross-certify. Otherwise, use the same
          * standard wording as any other weak crypto primitive.
          */
-        betteralgs = NULL;
         for (j = 0; j < s->n_uncert_hostkeys; j++) {
             const struct ssh_signkey_with_user_pref_id *hktype =
                 &ssh2_hostkey_algs[s->uncert_hostkeys[j]];
@@ -1538,19 +1538,16 @@ static void ssh2_transport_process_queue(PacketProtocolLayer *ppl)
                 }
             }
             if (better) {
-                if (betteralgs) {
+                sgrowarray(betteralgs, bettersize, nbetter);
-                    char *old_ba = betteralgs;
+                betteralgs[nbetter++] = hktype->alg->ssh_id;
-                    betteralgs = dupcat(betteralgs, ",", hktype->alg->ssh_id);
-                    sfree(old_ba);
-                } else {
-                    betteralgs = dupstr(hktype->alg->ssh_id);
-                }
             }
         }
         if (betteralgs) {
             /* Use the special warning prompt that lets us provide
              * a list of better algorithms */
-            s->spr = seat_confirm_weak_cached_hostkey(
+            sgrowarray(betteralgs, bettersize, nbetter);
+            betteralgs[nbetter] = NULL;
+            s->spr = confirm_weak_cached_hostkey(
                 ppl_get_iseat(&s->ppl), s->hostkey_alg->ssh_id, betteralgs,
                 ssh2_transport_dialog_callback, s);
             sfree(betteralgs);
@@ -2389,7 +2386,7 @@ static int ca_blob_compare(void *av, void *bv)
 }
 
 /*
- * Wrapper on seat_confirm_weak_crypto_primitive(), which uses the
+ * Wrapper on confirm_weak_crypto_primitive(), which uses the
  * tree234 s->weak_algorithms_consented_to to ensure we ask at most
  * once about any given crypto primitive.
  */
@@ -2401,7 +2398,7 @@ static SeatPromptResult ssh2_transport_confirm_weak_crypto_primitive(
         return SPR_OK;
     add234(s->weak_algorithms_consented_to, (void *)alg);
 
-    return seat_confirm_weak_crypto_primitive(
+    return confirm_weak_crypto_primitive(
         ppl_get_iseat(&s->ppl), type, name, ssh2_transport_dialog_callback, s);
 }
 

stubs/null-seat.c

@@ -26,11 +26,11 @@ SeatPromptResult nullseat_confirm_ssh_host_key(
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 { return SPR_SW_ABORT("this seat can't handle interactive prompts"); }
 SeatPromptResult nullseat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 { return SPR_SW_ABORT("this seat can't handle interactive prompts"); }
 SeatPromptResult nullseat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 { return SPR_SW_ABORT("this seat can't handle interactive prompts"); }
 bool nullseat_is_never_utf8(Seat *seat) { return false; }
@@ -60,6 +60,8 @@ const SeatDialogPromptDescriptions *nullseat_prompt_descriptions(Seat *seat)
         .hk_connect_once_action = "",
         .hk_cancel_action = "",
         .hk_cancel_action_Participle = "",
+        .weak_accept_action = "",
+        .weak_cancel_action = "",
     };
     return &descs;
 }

unix/console.c

@@ -102,20 +102,18 @@ static int block_and_read(int fd, void *buf, size_t len)
     return ret;
 }
 
-SeatPromptResult console_confirm_ssh_host_key(
+/*
-    Seat *seat, const char *host, int port, const char *keytype,
+ * Helper function to print the message from a SeatDialogText. Returns
-    char *keystr, SeatDialogText *text, HelpCtx helpctx,
+ * the final prompt to print on the input line, or NULL if a
-    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+ * batch-mode abort is needed. In the latter case it will have printed
+ * the abort text already.
+ */
+static const char *console_print_seatdialogtext(SeatDialogText *text)
 {
-    char line[32];
-    struct termios cf;
     const char *prompt = NULL;
-
     stdio_sink errsink[1];
     stdio_sink_init(errsink, stderr);
 
-    premsg(&cf);
-
     for (SeatDialogTextItem *item = text->items,
              *end = item+text->nitems; item < end; item++) {
         switch (item->type) {
@@ -135,8 +133,7 @@ SeatPromptResult console_confirm_ssh_host_key(
             if (console_batch_mode) {
                 fprintf(stderr, "%s\n", item->text);
                 fflush(stderr);
-                postmsg(&cf);
+                return NULL;
-                return SPR_SW_ABORT("Cannot confirm a host key in batch mode");
             }
             break;
           case SDT_PROMPT:
@@ -146,7 +143,26 @@ SeatPromptResult console_confirm_ssh_host_key(
             break;
         }
     }
+
     assert(prompt); /* something in the SeatDialogText should have set this */
+    return prompt;
+}
+
+SeatPromptResult console_confirm_ssh_host_key(
+    Seat *seat, const char *host, int port, const char *keytype,
+    char *keystr, SeatDialogText *text, HelpCtx helpctx,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+{
+    char line[32];
+    struct termios cf;
+
+    premsg(&cf);
+
+    const char *prompt = console_print_seatdialogtext(text);
+    if (!prompt) {
+        postmsg(&cf);
+        return SPR_SW_ABORT("Cannot confirm a host key in batch mode");
+    }
 
     while (true) {
         fprintf(stderr,
@@ -202,23 +218,22 @@ SeatPromptResult console_confirm_ssh_host_key(
 }
 
 SeatPromptResult console_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     char line[32];
     struct termios cf;
 
     premsg(&cf);
-    fprintf(stderr, weakcrypto_msg_common_fmt, algtype, algname);
 
-    if (console_batch_mode) {
+    const char *prompt = console_print_seatdialogtext(text);
-        fputs(console_abandoned_msg, stderr);
+    if (!prompt) {
         postmsg(&cf);
         return SPR_SW_ABORT("Cannot confirm a weak crypto primitive "
                             "in batch mode");
     }
 
-    fputs(console_continue_prompt, stderr);
+    fprintf(stderr, "%s (y/n) ", prompt);
     fflush(stderr);
 
     {
@@ -244,23 +259,22 @@ SeatPromptResult console_confirm_weak_crypto_primitive(
 }
 
 SeatPromptResult console_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     char line[32];
     struct termios cf;
 
     premsg(&cf);
-    fprintf(stderr, weakhk_msg_common_fmt, algname, betteralgs);
 
-    if (console_batch_mode) {
+    const char *prompt = console_print_seatdialogtext(text);
-        fputs(console_abandoned_msg, stderr);
+    if (!prompt) {
         postmsg(&cf);
         return SPR_SW_ABORT("Cannot confirm a weak cached host key "
                             "in batch mode");
     }
 
-    fputs(console_continue_prompt, stderr);
+    fprintf(stderr, "%s (y/n) ", prompt);
     fflush(stderr);
 
     {

unix/dialog.c

@@ -3609,10 +3609,54 @@ const SeatDialogPromptDescriptions *gtk_seat_prompt_descriptions(Seat *seat)
         .hk_connect_once_action = "press \"Connect Once\"",
         .hk_cancel_action = "press \"Cancel\"",
         .hk_cancel_action_Participle = "Pressing \"Cancel\"",
+        .weak_accept_action = "press \"Yes\"",
+        .weak_cancel_action = "press \"No\"",
     };
     return &descs;
 }
 
+/*
+ * Format a SeatDialogText into a strbuf, also adjusting the box width
+ * to cope with displayed text. Returns the dialog box title.
+ */
+static const char *gtk_format_seatdialogtext(
+    SeatDialogText *text, strbuf *dlg_text, int *width)
+{
+    const char *dlg_title = NULL;
+
+    for (SeatDialogTextItem *item = text->items,
+             *end = item + text->nitems; item < end; item++) {
+        switch (item->type) {
+          case SDT_PARA:
+            put_fmt(dlg_text, "%s\n\n", item->text);
+            break;
+          case SDT_DISPLAY: {
+            put_fmt(dlg_text, "%s\n\n", item->text);
+            int thiswidth = string_width(item->text);
+            if (*width < thiswidth)
+                *width = thiswidth;
+            break;
+          }
+          case SDT_SCARY_HEADING:
+            /* Can't change font size or weight in this context */
+            put_fmt(dlg_text, "%s\n\n", item->text);
+            break;
+          case SDT_TITLE:
+            dlg_title = item->text;
+            break;
+          default:
+            break;
+        }
+    }
+
+    /*
+     * Trim trailing newlines.
+     */
+    while (strbuf_chomp(dlg_text, '\n'));
+
+    return dlg_title;
+}
+
 SeatPromptResult gtk_seat_confirm_ssh_host_key(
     Seat *seat, const char *host, int port, const char *keytype,
     char *keystr, SeatDialogText *text, HelpCtx helpctx,
@@ -3627,35 +3671,9 @@ SeatPromptResult gtk_seat_confirm_ssh_host_key(
         button_array_hostkey, lenof(button_array_hostkey),
     };
 
-    const char *dlg_title = NULL;
-    strbuf *dlg_text = strbuf_new();
     int width = string_width("default dialog width determination string");
-
+    strbuf *dlg_text = strbuf_new();
-    for (SeatDialogTextItem *item = text->items,
+    const char *dlg_title = gtk_format_seatdialogtext(text, dlg_text, &width);
-             *end = item + text->nitems; item < end; item++) {
-        switch (item->type) {
-          case SDT_PARA:
-            put_fmt(dlg_text, "%s\n\n", item->text);
-            break;
-          case SDT_DISPLAY: {
-            put_fmt(dlg_text, "%s\n\n", item->text);
-            int thiswidth = string_width(item->text);
-            if (width < thiswidth)
-                width = thiswidth;
-            break;
-          }
-          case SDT_SCARY_HEADING:
-            /* Can't change font size or weight in this context */
-            put_fmt(dlg_text, "%s\n\n", item->text);
-            break;
-          case SDT_TITLE:
-            dlg_title = item->text;
-            break;
-          default:
-            break;
-        }
-    }
-    while (strbuf_chomp(dlg_text, '\n'));
 
     GtkWidget *mainwin, *msgbox;
 
@@ -3752,19 +3770,16 @@ static void simple_prompt_result_spr_callback(void *vctx, int result)
  * below the configured 'warn' threshold).
  */
 SeatPromptResult gtk_seat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
-    static const char msg[] =
-        "The first %s supported by the server is "
-        "%s, which is below the configured warning threshold.\n"
-        "Continue with connection?";
-
-    char *text;
     struct simple_prompt_result_spr_ctx *result_ctx;
     GtkWidget *mainwin, *msgbox;
 
-    text = dupprintf(msg, algtype, algname);
+    int width = string_width("Reasonably long line of text "
+                             "as a width template");
+    strbuf *dlg_text = strbuf_new();
+    const char *dlg_title = gtk_format_seatdialogtext(text, dlg_text, &width);
 
     result_ctx = snew(struct simple_prompt_result_spr_ctx);
     result_ctx->callback = callback;
@@ -3774,33 +3789,26 @@ SeatPromptResult gtk_seat_confirm_weak_crypto_primitive(
 
     mainwin = GTK_WIDGET(gtk_seat_get_window(seat));
     msgbox = create_message_box(
-        mainwin, "PuTTY Security Alert", text,
+        mainwin, dlg_title, dlg_text->s, width, false,
-        string_width("Reasonably long line of text as a width template"),
+        &buttons_yn, simple_prompt_result_spr_callback, result_ctx);
-        false, &buttons_yn, simple_prompt_result_spr_callback, result_ctx);
     register_dialog(seat, result_ctx->dialog_slot, msgbox);
 
-    sfree(text);
+    strbuf_free(dlg_text);
 
     return SPR_INCOMPLETE;
 }
 
 SeatPromptResult gtk_seat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
-    static const char msg[] =
-        "The first host key type we have stored for this server\n"
-        "is %s, which is below the configured warning threshold.\n"
-        "The server also provides the following types of host key\n"
-        "above the threshold, which we do not have stored:\n"
-        "%s\n"
-        "Continue with connection?";
-
-    char *text;
     struct simple_prompt_result_spr_ctx *result_ctx;
     GtkWidget *mainwin, *msgbox;
 
-    text = dupprintf(msg, algname, betteralgs);
+    int width = string_width("is ecdsa-nistp521, which is below the configured"
+                             " warning threshold.");
+    strbuf *dlg_text = strbuf_new();
+    const char *dlg_title = gtk_format_seatdialogtext(text, dlg_text, &width);
 
     result_ctx = snew(struct simple_prompt_result_spr_ctx);
     result_ctx->callback = callback;
@@ -3810,13 +3818,11 @@ SeatPromptResult gtk_seat_confirm_weak_cached_hostkey(
 
     mainwin = GTK_WIDGET(gtk_seat_get_window(seat));
     msgbox = create_message_box(
-        mainwin, "PuTTY Security Alert", text,
+        mainwin, dlg_title, dlg_text->s, width, false,
-        string_width("is ecdsa-nistp521, which is below the configured"
+        &buttons_yn, simple_prompt_result_spr_callback, result_ctx);
-                     " warning threshold."),
-        false, &buttons_yn, simple_prompt_result_spr_callback, result_ctx);
     register_dialog(seat, result_ctx->dialog_slot, msgbox);
 
-    sfree(text);
+    strbuf_free(dlg_text);
 
     return SPR_INCOMPLETE;
 }

unix/platform.h

@@ -225,10 +225,10 @@ SeatPromptResult gtk_seat_confirm_ssh_host_key(
     char *keystr, SeatDialogText *text, HelpCtx helpctx,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult gtk_seat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult gtk_seat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 const SeatDialogPromptDescriptions *gtk_seat_prompt_descriptions(Seat *seat);
 #ifdef MAY_REFER_TO_GTK_IN_HEADERS

utils/tempseat.c

@@ -255,7 +255,7 @@ static SeatPromptResult tempseat_confirm_ssh_host_key(
 }
 
 static SeatPromptResult tempseat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     unreachable("confirm_weak_crypto_primitive "
@@ -263,7 +263,7 @@ static SeatPromptResult tempseat_confirm_weak_crypto_primitive(
 }
 
 static SeatPromptResult tempseat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     unreachable("confirm_weak_cached_hostkey "

windows/console.c

@@ -32,20 +32,18 @@ void console_print_error_msg(const char *prefix, const char *msg)
     fflush(stderr);
 }
 
-SeatPromptResult console_confirm_ssh_host_key(
+/*
-    Seat *seat, const char *host, int port, const char *keytype,
+ * Helper function to print the message from a SeatDialogText. Returns
-    char *keystr, SeatDialogText *text, HelpCtx helpctx,
+ * the final prompt to print on the input line, or NULL if a
-    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+ * batch-mode abort is needed. In the latter case it will have printed
+ * the abort text already.
+ */
+static const char *console_print_seatdialogtext(SeatDialogText *text)
 {
-    HANDLE hin;
-    DWORD savemode, i;
     const char *prompt = NULL;
-
     stdio_sink errsink[1];
     stdio_sink_init(errsink, stderr);
 
-    char line[32];
-
     for (SeatDialogTextItem *item = text->items,
              *end = item+text->nitems; item < end; item++) {
         switch (item->type) {
@@ -65,7 +63,7 @@ SeatPromptResult console_confirm_ssh_host_key(
             if (console_batch_mode) {
                 fprintf(stderr, "%s\n", item->text);
                 fflush(stderr);
-                return SPR_SW_ABORT("Cannot confirm a host key in batch mode");
+                return NULL;
             }
             break;
           case SDT_PROMPT:
@@ -76,6 +74,22 @@ SeatPromptResult console_confirm_ssh_host_key(
         }
     }
     assert(prompt); /* something in the SeatDialogText should have set this */
+    return prompt;
+}
+
+SeatPromptResult console_confirm_ssh_host_key(
+    Seat *seat, const char *host, int port, const char *keytype,
+    char *keystr, SeatDialogText *text, HelpCtx helpctx,
+    void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
+{
+    HANDLE hin;
+    DWORD savemode, i;
+
+    const char *prompt = console_print_seatdialogtext(text);
+    if (!prompt)
+        return SPR_SW_ABORT("Cannot confirm a host key in batch mode");
+
+    char line[32];
 
     while (true) {
         fprintf(stderr,
@@ -128,23 +142,20 @@ SeatPromptResult console_confirm_ssh_host_key(
 }
 
 SeatPromptResult console_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     HANDLE hin;
     DWORD savemode, i;
 
-    char line[32];
+    const char *prompt = console_print_seatdialogtext(text);
-
+    if (!prompt)
-    fprintf(stderr, weakcrypto_msg_common_fmt, algtype, algname);
-
-    if (console_batch_mode) {
-        fputs(console_abandoned_msg, stderr);
         return SPR_SW_ABORT("Cannot confirm a weak crypto primitive "
                             "in batch mode");
-    }
 
-    fputs(console_continue_prompt, stderr);
+    char line[32];
+
+    fprintf(stderr, "%s (y/n) ", prompt);
     fflush(stderr);
 
     hin = GetStdHandle(STD_INPUT_HANDLE);
@@ -163,23 +174,20 @@ SeatPromptResult console_confirm_weak_crypto_primitive(
 }
 
 SeatPromptResult console_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
     HANDLE hin;
     DWORD savemode, i;
 
-    char line[32];
+    const char *prompt = console_print_seatdialogtext(text);
-
+    if (!prompt)
-    fprintf(stderr, weakhk_msg_common_fmt, algname, betteralgs);
-
-    if (console_batch_mode) {
-        fputs(console_abandoned_msg, stderr);
         return SPR_SW_ABORT("Cannot confirm a weak cached host key "
                             "in batch mode");
-    }
 
-    fputs(console_continue_prompt, stderr);
+    char line[32];
+
+    fprintf(stderr, "%s (y/n) ", prompt);
     fflush(stderr);
 
     hin = GetStdHandle(STD_INPUT_HANDLE);

windows/dialog.c

@@ -963,6 +963,39 @@ static INT_PTR HostKeyMoreInfoProc(HWND hwnd, UINT msg, WPARAM wParam,
     return 0;
 }
 
+static const char *process_seatdialogtext(
+    strbuf *dlg_text, const char **scary_heading, SeatDialogText *text)
+{
+    const char *dlg_title = "";
+
+    for (SeatDialogTextItem *item = text->items,
+             *end = item + text->nitems; item < end; item++) {
+        switch (item->type) {
+          case SDT_PARA:
+            put_fmt(dlg_text, "%s\r\n\r\n", item->text);
+            break;
+          case SDT_DISPLAY:
+            put_fmt(dlg_text, "%s\r\n\r\n", item->text);
+            break;
+          case SDT_SCARY_HEADING:
+            assert(scary_heading != NULL && "only expect a scary heading if "
+                   "the dialog has somewhere to put it");
+            *scary_heading = item->text;
+            break;
+          case SDT_TITLE:
+            dlg_title = item->text;
+            break;
+          default:
+            break;
+        }
+    }
+
+    /* Trim any trailing newlines */
+    while (strbuf_chomp(dlg_text, '\r') || strbuf_chomp(dlg_text, '\n'));
+
+    return dlg_title;
+}
+
 static INT_PTR HostKeyDialogProc(HWND hwnd, UINT msg,
                                  WPARAM wParam, LPARAM lParam, void *vctx)
 {
@@ -971,32 +1004,15 @@ static INT_PTR HostKeyDialogProc(HWND hwnd, UINT msg,
     switch (msg) {
       case WM_INITDIALOG: {
         strbuf *dlg_text = strbuf_new();
-        const char *dlg_title = "";
+        const char *scary_heading = NULL;
-        ctx->has_title = false;
+        const char *dlg_title = process_seatdialogtext(
-        LPCTSTR iconid = IDI_QUESTION;
+            dlg_text, &scary_heading, ctx->text);
 
-        for (SeatDialogTextItem *item = ctx->text->items,
+        LPCTSTR iconid = IDI_QUESTION;
-                 *end = item + ctx->text->nitems; item < end; item++) {
+        if (scary_heading) {
-            switch (item->type) {
+            SetDlgItemText(hwnd, IDC_HK_TITLE, scary_heading);
-              case SDT_PARA:
+            iconid = IDI_WARNING;
-                put_fmt(dlg_text, "%s\r\n\r\n", item->text);
-                break;
-              case SDT_DISPLAY:
-                put_fmt(dlg_text, "%s\r\n\r\n", item->text);
-                break;
-              case SDT_SCARY_HEADING:
-                SetDlgItemText(hwnd, IDC_HK_TITLE, item->text);
-                iconid = IDI_WARNING;
-                ctx->has_title = true;
-                break;
-              case SDT_TITLE:
-                dlg_title = item->text;
-                break;
-              default:
-                break;
-            }
         }
-        while (strbuf_chomp(dlg_text, '\r') || strbuf_chomp(dlg_text, '\n'));
 
         SetDlgItemText(hwnd, IDC_HK_TEXT, dlg_text->s);
         MakeDlgItemBorderless(hwnd, IDC_HK_TEXT);
@@ -1135,6 +1151,8 @@ const SeatDialogPromptDescriptions *win_seat_prompt_descriptions(Seat *seat)
         .hk_connect_once_action = "press \"Connect Once\"",
         .hk_cancel_action = "press \"Cancel\"",
         .hk_cancel_action_Participle = "Pressing \"Cancel\"",
+        .weak_accept_action = "press \"Yes\"",
+        .weak_cancel_action = "press \"No\"",
     };
     return &descs;
 }
@@ -1169,25 +1187,17 @@ SeatPromptResult win_seat_confirm_ssh_host_key(
  * below the configured 'warn' threshold).
  */
 SeatPromptResult win_seat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
-    static const char mbtitle[] = "%s Security Alert";
+    strbuf *dlg_text = strbuf_new();
-    static const char msg[] =
+    const char *dlg_title = process_seatdialogtext(dlg_text, NULL, text);
-        "The first %s supported by the server\n"
-        "is %s, which is below the configured\n"
-        "warning threshold.\n"
-        "Do you want to continue with this connection?\n";
-    char *message, *title;
-    int mbret;
 
-    message = dupprintf(msg, algtype, algname);
+    int mbret = MessageBox(NULL, dlg_text->s, dlg_title,
-    title = dupprintf(mbtitle, appname);
+                           MB_ICONWARNING | MB_YESNO | MB_DEFBUTTON2);
-    mbret = MessageBox(NULL, message, title,
-                       MB_ICONWARNING | MB_YESNO | MB_DEFBUTTON2);
     socket_reselect_all();
-    sfree(message);
+    strbuf_free(dlg_text);
-    sfree(title);
+
     if (mbret == IDYES)
         return SPR_OK;
     else
@@ -1195,27 +1205,17 @@ SeatPromptResult win_seat_confirm_weak_crypto_primitive(
 }
 
 SeatPromptResult win_seat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx)
 {
-    static const char mbtitle[] = "%s Security Alert";
+    strbuf *dlg_text = strbuf_new();
-    static const char msg[] =
+    const char *dlg_title = process_seatdialogtext(dlg_text, NULL, text);
-        "The first host key type we have stored for this server\n"
-        "is %s, which is below the configured warning threshold.\n"
-        "The server also provides the following types of host key\n"
-        "above the threshold, which we do not have stored:\n"
-        "%s\n"
-        "Do you want to continue with this connection?\n";
-    char *message, *title;
-    int mbret;
 
-    message = dupprintf(msg, algname, betteralgs);
+    int mbret = MessageBox(NULL, dlg_text->s, dlg_title,
-    title = dupprintf(mbtitle, appname);
+                           MB_ICONWARNING | MB_YESNO | MB_DEFBUTTON2);
-    mbret = MessageBox(NULL, message, title,
-                       MB_ICONWARNING | MB_YESNO | MB_DEFBUTTON2);
     socket_reselect_all();
-    sfree(message);
+    strbuf_free(dlg_text);
-    sfree(title);
+
     if (mbret == IDYES)
         return SPR_OK;
     else

windows/platform.h

@@ -237,10 +237,10 @@ SeatPromptResult win_seat_confirm_ssh_host_key(
     char *keystr, SeatDialogText *text, HelpCtx helpctx,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult win_seat_confirm_weak_crypto_primitive(
-    Seat *seat, const char *algtype, const char *algname,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 SeatPromptResult win_seat_confirm_weak_cached_hostkey(
-    Seat *seat, const char *algname, const char *betteralgs,
+    Seat *seat, SeatDialogText *text,
     void (*callback)(void *ctx, SeatPromptResult result), void *ctx);
 const SeatDialogPromptDescriptions *win_seat_prompt_descriptions(Seat *seat);