diff --git a/NEWS b/NEWS
index 363e918da1..68bae1c407 100644
--- a/NEWS
+++ b/NEWS
@@ -59,6 +59,14 @@ Deprecated and removed features, and other changes affecting compatibility:
 
 * The tilegx*-*-linux-gnu configurations are no longer supported.
 
+* The functions 'encrypt', 'encrypt_r', 'setkey', 'setkey_r', 'cbc_crypt',
+  'ecb_crypt', and 'des_setparity' are deprecated.  They encrypt and decrypt
+  data with the DES block cipher, which is no longer considered secure.
+  Also, encrypt, encrypt_r, setkey, and setkey_r require awkward pre- and
+  post-processing of the encryption key and data to be encrypted, and
+  encrypt and setkey are not thread-safe.  Software that still uses these
+  functions should switch to a modern cryptography library, such as GnuTLS.
+
 Changes to build and runtime requirements:
 
   [Add changes to build and runtime requirements here]
diff --git a/crypt/Makefile b/crypt/Makefile
index 303800df73..e122bcebf0 100644
--- a/crypt/Makefile
+++ b/crypt/Makefile
@@ -32,6 +32,9 @@ libcrypt-routines := crypt-entry md5-crypt sha256-crypt sha512-crypt crypt \
 
 tests := cert md5c-test sha256c-test sha512c-test badsalttest
 
+# cert.c tests the deprecated setkey/encrypt interface
+CFLAGS-cert.c = -Wno-deprecated-declarations
+
 ifeq ($(crypt-in-libc),yes)
 routines += $(libcrypt-routines)
 endif
diff --git a/crypt/crypt.h b/crypt/crypt.h
index 5da098b715..22cf13ff89 100644
--- a/crypt/crypt.h
+++ b/crypt/crypt.h
@@ -32,13 +32,18 @@ __BEGIN_DECLS
 extern char *crypt (const char *__key, const char *__salt)
      __THROW __nonnull ((1, 2));
 
-/* Setup DES tables according KEY.  */
-extern void setkey (const char *__key) __THROW __nonnull ((1));
+/* Set the encryption key for subsequent calls to 'encrypt'.
+   This function should not be used in new programs, because the cipher
+   it uses is DES, which is unacceptably weak by modern standards.  */
+extern void setkey (const char *__key)
+     __THROW __nonnull ((1)) __attribute_deprecated__;
 
 /* Encrypt data in BLOCK in place if EDFLAG is zero; otherwise decrypt
-   block in place.  */
+   block in place.  The key is controlled by 'setkey'.
+   This function should not be used in new programs, because the cipher
+   it uses is DES, which is unacceptably weak by modern standards.  */
 extern void encrypt (char *__glibc_block, int __edflag)
-     __THROW __nonnull ((1));
+     __THROW __nonnull ((1)) __attribute_deprecated__;
 
 #ifdef __USE_GNU
 /* Reentrant versions of the functions above.  The additional argument
@@ -63,11 +68,11 @@ extern char *crypt_r (const char *__key, const char *__salt,
 
 extern void setkey_r (const char *__key,
 		      struct crypt_data * __restrict __data)
-     __THROW __nonnull ((1, 2));
+     __THROW __nonnull ((1, 2)) __attribute_deprecated__;
 
 extern void encrypt_r (char *__glibc_block, int __edflag,
 		       struct crypt_data * __restrict __data)
-     __THROW __nonnull ((1, 3));
+     __THROW __nonnull ((1, 3)) __attribute_deprecated__;
 #endif
 
 __END_DECLS
diff --git a/posix/unistd.h b/posix/unistd.h
index 4d149f9945..5d4e07f6c8 100644
--- a/posix/unistd.h
+++ b/posix/unistd.h
@@ -1127,10 +1127,12 @@ extern char *crypt (const char *__key, const char *__salt)
      __THROW __nonnull ((1, 2));
 
 /* Encrypt data in BLOCK in place if EDFLAG is zero; otherwise decrypt
-   block in place.  */
-extern void encrypt (char *__glibc_block, int __edflag)
-     __THROW __nonnull ((1));
+   block in place.  The key is controlled by 'setkey', in stdlib.h.
 
+   This function should not be used in new programs, because the cipher
+   it uses is DES, which is unacceptably weak by modern standards.  */
+extern void encrypt (char *__glibc_block, int __edflag)
+     __THROW __nonnull ((1)) __attribute_deprecated__;
 
 /* Swab pairs bytes in the first N bytes of the area pointed to by
    FROM and copy the result to TO.  The value of TO must not be in the
diff --git a/stdlib/stdlib.h b/stdlib/stdlib.h
index 6b1ead31e0..5b104bcc51 100644
--- a/stdlib/stdlib.h
+++ b/stdlib/stdlib.h
@@ -959,8 +959,13 @@ extern int getsubopt (char **__restrict __optionp,
 
 
 #ifdef __USE_XOPEN
-/* Setup DES tables according KEY.  */
-extern void setkey (const char *__key) __THROW __nonnull ((1));
+/* Set the encryption key for subsequent calls to 'encrypt', which is
+   declared in unistd.h.
+
+   This function should not be used in new programs, because the cipher
+   it uses is DES, which is unacceptably weak by modern standards.  */
+extern void setkey (const char *__key)
+     __THROW __nonnull ((1)) __attribute_deprecated__;
 #endif
 
 
diff --git a/sunrpc/Makefile b/sunrpc/Makefile
index 8f2a3c8213..07fb90de6b 100644
--- a/sunrpc/Makefile
+++ b/sunrpc/Makefile
@@ -156,6 +156,15 @@ CFLAGS-pmap_rmt.c += -fexceptions
 CFLAGS-clnt_perr.c += -fexceptions
 CFLAGS-openchild.c += -fexceptions
 
+# These files implement Secure RPC authentication using DES, which is
+# no longer secure and has had some of the associated functions tagged
+# __attribute_deprecated__.
+CFLAGS-auth_des.c += -Wno-deprecated-declarations
+CFLAGS-des_crypt.c += -Wno-deprecated-declarations
+CFLAGS-des_soft.c += -Wno-deprecated-declarations
+CFLAGS-svcauth_des.c += -Wno-deprecated-declarations
+CFLAGS-xcrypt.c += -Wno-deprecated-declarations
+
 sunrpc-CPPFLAGS = -D_RPC_THREAD_SAFE_
 CPPFLAGS += $(sunrpc-CPPFLAGS)
 BUILD_CPPFLAGS += $(sunrpc-CPPFLAGS)
diff --git a/sunrpc/rpc/des_crypt.h b/sunrpc/rpc/des_crypt.h
index 77cca3cbed..85875afa11 100644
--- a/sunrpc/rpc/des_crypt.h
+++ b/sunrpc/rpc/des_crypt.h
@@ -70,6 +70,10 @@ __BEGIN_DECLS
  * DESERR_NOHWDEVICE is returned if DES_HW was specified but
  * there was no hardware to do it on (the data will still be
  * encrypted though, in software).
+ *
+ * None of the functions in this header should be used in new programs,
+ * because the cipher they use is DES, which is unacceptably weak by
+ * modern standards.
  */
 
 
@@ -77,19 +81,20 @@ __BEGIN_DECLS
  * Cipher Block Chaining mode
  */
 extern int cbc_crypt (char *__key, char *__buf, unsigned __len,
-		      unsigned __mode, char *__ivec) __THROW;
+		      unsigned __mode, char *__ivec)
+  __THROW __attribute_deprecated__;
 
 /*
  * Electronic Code Book mode
  */
 extern int ecb_crypt (char *__key, char *__buf, unsigned __len,
-		      unsigned __mode) __THROW;
+		      unsigned __mode) __THROW __attribute_deprecated__;
 
 /*
  * Set des parity for a key.
  * DES parity is odd and in the low bit of each byte
  */
-extern void des_setparity (char *__key) __THROW;
+extern void des_setparity (char *__key) __THROW __attribute_deprecated__;
 
 __END_DECLS
 
