diff --git a/cmake/cmake.h.in b/cmake/cmake.h.in
index f8fcbc58..3d36b3d0 100644
--- a/cmake/cmake.h.in
+++ b/cmake/cmake.h.in
@@ -60,3 +60,4 @@
 #cmakedefine01 HAVE_NEON_SHA512
 #cmakedefine01 HAVE_NEON_SHA512_INTRINSICS
 #cmakedefine01 USE_ARM64_NEON_H
+#cmakedefine01 HAVE_ARM_DIT
diff --git a/cmdgen.c b/cmdgen.c
index 295cdd77..9883fd26 100644
--- a/cmdgen.c
+++ b/cmdgen.c
@@ -264,6 +264,8 @@ int main(int argc, char **argv)
     ppk_save_parameters params = ppk_save_default_parameters;
     FingerprintType fptype = SSH_FPTYPE_DEFAULT;
 
+    enable_dit();
+
     if (is_interactive())
         progress_fp = stderr;
 
diff --git a/crypto/CMakeLists.txt b/crypto/CMakeLists.txt
index 6358569a..e57bb600 100644
--- a/crypto/CMakeLists.txt
+++ b/crypto/CMakeLists.txt
@@ -236,6 +236,12 @@ if(neon)
   endif()
 endif()
 
+test_compile_with_flags(HAVE_ARM_DIT
+  GNU_FLAGS -march=armv8.4-a
+  TEST_SOURCE "
+    int main(void) { asm volatile(\"msr dit, %0\" :: \"r\"(1)); }"
+  ADD_SOURCES_IF_SUCCESSFUL enable_dit.c)
+
 set(HAVE_AES_NI ${HAVE_AES_NI} PARENT_SCOPE)
 set(HAVE_SHA_NI ${HAVE_SHA_NI} PARENT_SCOPE)
 set(HAVE_SHAINTRIN_H ${HAVE_SHAINTRIN_H} PARENT_SCOPE)
@@ -243,3 +249,4 @@ set(HAVE_NEON_CRYPTO ${HAVE_NEON_CRYPTO} PARENT_SCOPE)
 set(HAVE_NEON_SHA512 ${HAVE_NEON_SHA512} PARENT_SCOPE)
 set(HAVE_NEON_SHA512_INTRINSICS ${HAVE_NEON_SHA512_INTRINSICS} PARENT_SCOPE)
 set(USE_ARM64_NEON_H ${USE_ARM64_NEON_H} PARENT_SCOPE)
+set(HAVE_ARM_DIT ${HAVE_ARM_DIT} PARENT_SCOPE)
diff --git a/crypto/enable_dit.c b/crypto/enable_dit.c
new file mode 100644
index 00000000..7c9ec4b4
--- /dev/null
+++ b/crypto/enable_dit.c
@@ -0,0 +1,24 @@
+/*
+ * Enable the PSTATE.DIT flag in AArch64, if available.
+ *
+ * This guarantees that data-processing instructions (or rather, a
+ * long list of specific ones) will have data-independent timing
+ * (hence the name). In other words, you want to turn this bit on if
+ * you're trying to do constant-time crypto.
+ *
+ * For maximum performance you'd want to turn this bit back off when
+ * doing any CPU-intensive stuff that _isn't_ cryptographic. That
+ * seems like a small concern in this code base, and carries the risk
+ * of losing track of whether it was on or not, so here we just enable
+ * it for the whole process. That's why there's only an enable_dit()
+ * function in this file and not a disable_dit() to go with it.
+ */
+
+#include "ssh.h"
+
+void enable_dit(void)
+{
+    if (!platform_dit_available())
+        return;
+    asm volatile("msr dit, %0" :: "r"(1));
+}
diff --git a/proxy/cproxy.c b/proxy/cproxy.c
index 40a2f609..4203eb5d 100644
--- a/proxy/cproxy.c
+++ b/proxy/cproxy.c
@@ -22,6 +22,7 @@ strbuf *chap_response(ptrlen challenge, ptrlen password)
 {
     strbuf *sb = strbuf_new_nm();
     const ssh2_macalg *alg = &ssh_hmac_md5;
+    enable_dit(); /* just in case main() forgot */
     mac_simple(alg, password, challenge, strbuf_append(sb, alg->len));
     return sb;
 }
@@ -75,6 +76,8 @@ void http_digest_response(BinarySink *bs, ptrlen username, ptrlen password,
     const ssh_hashalg *alg = httphashalgs[hash];
     size_t hashlen = httphashlengths[hash];
 
+    enable_dit(); /* just in case main() forgot */
+
     unsigned char ncbuf[4];
     PUT_32BIT_MSB_FIRST(ncbuf, nonce_count);
 
diff --git a/pscp.c b/pscp.c
index e3bbf1f3..c7c4623f 100644
--- a/pscp.c
+++ b/pscp.c
@@ -2274,6 +2274,7 @@ int psftp_main(CmdlineArgList *arglist)
     bool sanitise_stderr = true;
 
     sk_init();
+    enable_dit();
 
     /* Load Default Settings before doing anything else. */
     conf = conf_new();
diff --git a/psftp.c b/psftp.c
index 69044694..b33e29a9 100644
--- a/psftp.c
+++ b/psftp.c
@@ -2803,6 +2803,7 @@ int psftp_main(CmdlineArgList *arglist)
     Filename *batchfile = NULL;
 
     sk_init();
+    enable_dit();
 
     userhost = user = NULL;
 
diff --git a/ssh.h b/ssh.h
index 0dd3e6c0..0d31a4bc 100644
--- a/ssh.h
+++ b/ssh.h
@@ -1312,6 +1312,7 @@ bool platform_pmull_neon_available(void);
 bool platform_sha256_neon_available(void);
 bool platform_sha1_neon_available(void);
 bool platform_sha512_neon_available(void);
+bool platform_dit_available(void);
 
 /*
  * PuTTY version number formatted as an SSH version string.
@@ -2048,3 +2049,13 @@ enum {
     PLUGIN_NOTYPE = 256, /* packet too short to have a type */
     PLUGIN_EOF = 257 /* EOF from auth plugin */
 };
+
+/*
+ * CPU features for security
+ */
+
+#if HAVE_ARM_DIT
+void enable_dit(void);
+#else
+#define enable_dit() ((void)0)
+#endif
diff --git a/ssh/ssh.c b/ssh/ssh.c
index 87b1a039..6d72ed1c 100644
--- a/ssh/ssh.c
+++ b/ssh/ssh.c
@@ -954,6 +954,8 @@ static char *ssh_init(const BackendVtable *vt, Seat *seat,
 {
     Ssh *ssh;
 
+    enable_dit(); /* just in case main() forgot */
+
     ssh = snew(Ssh);
     memset(ssh, 0, sizeof(Ssh));
 
diff --git a/sshrand.c b/sshrand.c
index 7f3d6411..18720adc 100644
--- a/sshrand.c
+++ b/sshrand.c
@@ -93,8 +93,10 @@ void random_save_seed(void)
 
 void random_ref(void)
 {
-    if (!random_active++)
+    if (!random_active++) {
+        enable_dit(); /* just in case main() forgot */
         random_create(&ssh_sha256);
+    }
 }
 
 void random_setup_custom(const ssh_hashalg *hash)
diff --git a/stubs/no-dit.c b/stubs/no-dit.c
new file mode 100644
index 00000000..8ba3b23d
--- /dev/null
+++ b/stubs/no-dit.c
@@ -0,0 +1,15 @@
+/*
+ * Stub version of enable_dit(), included in applications like
+ * PuTTYtel and pterm which completely leave out the 'crypto' source
+ * directory.
+ */
+
+#include "ssh.h"
+
+#if HAVE_ARM_DIT
+
+void enable_dit(void)
+{
+}
+
+#endif
diff --git a/test/testcrypt.c b/test/testcrypt.c
index 328ffc47..fa3df196 100644
--- a/test/testcrypt.c
+++ b/test/testcrypt.c
@@ -1684,6 +1684,8 @@ int main(int argc, char **argv)
     const char *infile = NULL, *outfile = NULL;
     bool doing_opts = true;
 
+    enable_dit(); /* in case this is used as a crypto helper (Hyrum's Law) */
+
     while (--argc > 0) {
         char *p = *++argv;
 
diff --git a/test/testsc.c b/test/testsc.c
index b4950d8d..d38dd639 100644
--- a/test/testsc.c
+++ b/test/testsc.c
@@ -1879,6 +1879,11 @@ int main(int argc, char **argv)
     bool keep_outfiles = false;
     bool test_names_given = false;
 
+    /* One day, perhaps, if I ever get this test to work on Arm, we
+     * might actually _check_ DIT is enabled, and check we're sticking
+     * to the precise list of DIT-affected instructions */
+    enable_dit();
+
     memset(tests_to_run, 1, sizeof(tests_to_run));
     random_hash = ssh_hash_new(&ssh_sha256);
 
diff --git a/unix/CMakeLists.txt b/unix/CMakeLists.txt
index 4d8ef964..87ee6574 100644
--- a/unix/CMakeLists.txt
+++ b/unix/CMakeLists.txt
@@ -147,6 +147,7 @@ if(GTK_FOUND)
     ${CMAKE_SOURCE_DIR}/stubs/no-gss.c
     ${CMAKE_SOURCE_DIR}/stubs/no-ca-config.c
     ${CMAKE_SOURCE_DIR}/stubs/no-console.c
+    ${CMAKE_SOURCE_DIR}/stubs/no-dit.c
     ${CMAKE_SOURCE_DIR}/proxy/nosshproxy.c
     pty.c)
   be_list(pterm pterm)
@@ -163,6 +164,7 @@ if(GTK_FOUND)
       ${CMAKE_SOURCE_DIR}/stubs/no-gss.c
       ${CMAKE_SOURCE_DIR}/stubs/no-ca-config.c
       ${CMAKE_SOURCE_DIR}/stubs/no-console.c
+      ${CMAKE_SOURCE_DIR}/stubs/no-dit.c
       ${CMAKE_SOURCE_DIR}/proxy/nosshproxy.c
       pty.c)
     be_list(ptermapp pterm)
@@ -204,6 +206,7 @@ if(GTK_FOUND)
     ${CMAKE_SOURCE_DIR}/stubs/no-ca-config.c
     ${CMAKE_SOURCE_DIR}/stubs/no-console.c
     ${CMAKE_SOURCE_DIR}/stubs/no-rand.c
+    ${CMAKE_SOURCE_DIR}/stubs/no-dit.c
     ${CMAKE_SOURCE_DIR}/proxy/nocproxy.c
     ${CMAKE_SOURCE_DIR}/proxy/nosshproxy.c)
   be_list(puttytel PuTTYtel SERIAL OTHERBACKENDS)
diff --git a/unix/askpass.c b/unix/askpass.c
index a1143a8f..bdd62519 100644
--- a/unix/askpass.c
+++ b/unix/askpass.c
@@ -612,6 +612,8 @@ int main(int argc, char **argv)
     int exitcode;
     char *ret;
 
+    enable_dit(); /* maybe overkill, but we _are_ handling a secret */
+
     gtk_init(&argc, &argv);
 
     if (argc != 2) {
diff --git a/unix/main-gtk-application.c b/unix/main-gtk-application.c
index 3aaf6af7..cb9eeb1f 100644
--- a/unix/main-gtk-application.c
+++ b/unix/main-gtk-application.c
@@ -78,6 +78,7 @@ https://wiki.gnome.org/Projects/GTK%2B/OSX/Bundling has some links.
 #define MAY_REFER_TO_GTK_IN_HEADERS
 
 #include "putty.h"
+#include "ssh.h"
 #include "gtkmisc.h"
 #include "gtkcompat.h"
 
@@ -294,6 +295,8 @@ int main(int argc, char **argv)
 {
     int status;
 
+    enable_dit();
+
     /* Call the function in ux{putty,pterm}.c to do app-type
      * specific setup */
     setup(false);     /* false means we are not a one-session process */
diff --git a/unix/main-gtk-simple.c b/unix/main-gtk-simple.c
index a9a897ca..f1e57012 100644
--- a/unix/main-gtk-simple.c
+++ b/unix/main-gtk-simple.c
@@ -31,6 +31,7 @@
 #define MAY_REFER_TO_GTK_IN_HEADERS
 
 #include "putty.h"
+#include "ssh.h"
 #include "terminal.h"
 #include "gtkcompat.h"
 #include "unifont.h"
@@ -594,6 +595,7 @@ int main(int argc, char **argv)
     bool need_config_box;
 
     setlocale(LC_CTYPE, "");
+    enable_dit();
 
     /* Call the function in ux{putty,pterm}.c to do app-type
      * specific setup */
diff --git a/unix/pageant.c b/unix/pageant.c
index bd6d6d7f..9ac9a640 100644
--- a/unix/pageant.c
+++ b/unix/pageant.c
@@ -1313,6 +1313,8 @@ int main(int argc, char **argv)
     const char *symlink_path = NULL;
     FILE *logfp = NULL;
 
+    enable_dit();
+
     progname = argv[0];
 
     /*
diff --git a/unix/plink.c b/unix/plink.c
index b4a9749f..d5db2c2a 100644
--- a/unix/plink.c
+++ b/unix/plink.c
@@ -683,6 +683,8 @@ int main(int argc, char **argv)
     struct winsize size;
     const struct BackendVtable *backvt;
 
+    enable_dit();
+
     /*
      * Initialise port and protocol to sensible defaults. (These
      * will be overridden by more or less anything.)
diff --git a/unix/psusan.c b/unix/psusan.c
index 4e8693af..268dad25 100644
--- a/unix/psusan.c
+++ b/unix/psusan.c
@@ -348,6 +348,8 @@ int main(int argc, char **argv)
 
     Conf *conf = make_ssh_server_conf();
 
+    enable_dit();
+
     memset(&ssc, 0, sizeof(ssc));
 
     ssc.application_name = "PSUSAN";
diff --git a/unix/putty.c b/unix/putty.c
index 1ccc10b6..a1dd78c5 100644
--- a/unix/putty.c
+++ b/unix/putty.c
@@ -87,6 +87,7 @@ const unsigned cmdline_tooltype =
 void setup(bool single)
 {
     sk_init();
+    enable_dit();
     settings_set_default_protocol(be_default_protocol);
     /* Find the appropriate default port. */
     {
diff --git a/unix/sftp.c b/unix/sftp.c
index 9fb0bf6e..f2323ddd 100644
--- a/unix/sftp.c
+++ b/unix/sftp.c
@@ -576,6 +576,7 @@ const bool buildinfo_gtk_relevant = false;
  */
 int main(int argc, char *argv[])
 {
+    enable_dit();
     uxsel_init();
     CmdlineArgList *arglist = cmdline_arg_list_from_argv(argc, argv);
     return psftp_main(arglist);
diff --git a/unix/uppity.c b/unix/uppity.c
index 30501af7..5832ed98 100644
--- a/unix/uppity.c
+++ b/unix/uppity.c
@@ -650,6 +650,8 @@ int main(int argc, char **argv)
     struct cmdline_instance *ci = &instances[ninstances++];
     init_cmdline_instance(ci);
 
+    enable_dit();
+
     if (argc <= 1) {
         /*
          * We're going to terminate with an error message below,
diff --git a/unix/utils/arm_arch_queries.c b/unix/utils/arm_arch_queries.c
index c3dc286b..190ef71e 100644
--- a/unix/utils/arm_arch_queries.c
+++ b/unix/utils/arm_arch_queries.c
@@ -92,6 +92,21 @@ bool platform_sha512_neon_available(void)
 #endif
 }
 
+bool platform_dit_available(void)
+{
+#if defined HWCAP_DIT
+    return getauxval(AT_HWCAP) & HWCAP_DIT;
+#elif defined HWCAP2_DIT
+    return getauxval(AT_HWCAP2) & HWCAP2_DIT;
+#elif defined __APPLE__
+    SysctlResult res = test_sysctl_flag("hw.optional.arm.FEAT_DIT");
+    /* As above, treat 'missing' as enabled */
+    return res != SYSCTL_OFF;
+#else
+    return false;
+#endif
+}
+
 #else /* defined __arm__ || defined __aarch64__ */
 
 /*
diff --git a/windows/CMakeLists.txt b/windows/CMakeLists.txt
index aefcb9d2..960a440d 100644
--- a/windows/CMakeLists.txt
+++ b/windows/CMakeLists.txt
@@ -120,6 +120,7 @@ add_executable(puttytel
   ${CMAKE_SOURCE_DIR}/stubs/no-ca-config.c
   ${CMAKE_SOURCE_DIR}/stubs/no-console.c
   ${CMAKE_SOURCE_DIR}/stubs/no-rand.c
+  ${CMAKE_SOURCE_DIR}/stubs/no-dit.c
   ${CMAKE_SOURCE_DIR}/proxy/nocproxy.c
   ${CMAKE_SOURCE_DIR}/proxy/nosshproxy.c
   puttytel.rc)
@@ -159,6 +160,7 @@ if(HAVE_CONPTY)
     ${CMAKE_SOURCE_DIR}/stubs/no-ca-config.c
     ${CMAKE_SOURCE_DIR}/stubs/no-console.c
     ${CMAKE_SOURCE_DIR}/stubs/no-rand.c
+    ${CMAKE_SOURCE_DIR}/stubs/no-dit.c
     ${CMAKE_SOURCE_DIR}/proxy/nosshproxy.c
     pterm.rc)
   be_list(pterm pterm)
diff --git a/windows/pageant.c b/windows/pageant.c
index 202a10f8..a519926f 100644
--- a/windows/pageant.c
+++ b/windows/pageant.c
@@ -1520,6 +1520,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
     size_t nclkeys = 0, clkeysize = 0;
 
     dll_hijacking_protection();
+    enable_dit();
 
     hinst = inst;
 
diff --git a/windows/plink.c b/windows/plink.c
index 30779cef..face662f 100644
--- a/windows/plink.c
+++ b/windows/plink.c
@@ -296,6 +296,7 @@ int main(int argc, char **argv)
     const struct BackendVtable *vt;
 
     dll_hijacking_protection();
+    enable_dit();
 
     /*
      * Initialise port and protocol to sensible defaults. (These
diff --git a/windows/puttygen.c b/windows/puttygen.c
index c5115c06..8dcf666b 100644
--- a/windows/puttygen.c
+++ b/windows/puttygen.c
@@ -2370,6 +2370,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
     struct InitialParams params[1];
 
     dll_hijacking_protection();
+    enable_dit();
 
     init_common_controls();
     hinst = inst;
diff --git a/windows/sftp.c b/windows/sftp.c
index fb3658d7..64c1daf6 100644
--- a/windows/sftp.c
+++ b/windows/sftp.c
@@ -649,6 +649,7 @@ int main(int argc, char *argv[])
     int ret;
 
     dll_hijacking_protection();
+    enable_dit();
 
     CmdlineArgList *arglist = cmdline_arg_list_from_GetCommandLineW();
     ret = psftp_main(arglist);
diff --git a/windows/utils/arm_arch_queries.c b/windows/utils/arm_arch_queries.c
index b0193276..87728e10 100644
--- a/windows/utils/arm_arch_queries.c
+++ b/windows/utils/arm_arch_queries.c
@@ -43,3 +43,11 @@ bool platform_sha512_neon_available(void)
      * SHA-512 architecture extension. */
     return false;
 }
+
+bool platform_dit_available(void)
+{
+    /* As of 2024-12-17, as far as I can tell from docs.microsoft.com,
+     * Windows on Arm does not yet provide a PF_ARM_V8_* flag for the
+     * DIT bit in PSTATE. */
+    return false;
+}
diff --git a/windows/window.c b/windows/window.c
index b2ac0adb..efc028e9 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -448,6 +448,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
     int guess_width, guess_height;
 
     dll_hijacking_protection();
+    enable_dit();
 
     hinst = inst;
     hprev = prev;