diff -r c79fd57f86b6 Lib/test/test_codecencodings_cn.py
--- a/Lib/test/test_codecencodings_cn.py
+++ b/Lib/test/test_codecencodings_cn.py
@@ -49,6 +49,8 @@ class Test_GB18030(multibytecodec_support.TestBase
         (b"abc\x84\x32\x80\x80def", "replace", 'abc\ufffd2\ufffd\ufffddef'),
         (b"abc\x81\x30\x81\x30def", "strict", 'abc\x80def'),
         (b"abc\x86\x30\x81\x30def", "replace", 'abc\ufffd0\ufffd0def'),
+        # issue24117
+        (b"\x81\x30\xFF\x30", "strict",  None),
     )
     has_iso10646 = True
 
@@ -81,6 +83,10 @@ class Test_HZ(multibytecodec_support.TestBase, uni
         (b'ab~{\x81\x81\x41\x44~}cd', 'replace', 'ab\uFFFD\uFFFD\u804Acd'),
         (b'ab~{\x41\x44~}cd', 'replace', 'ab\u804Acd'),
         (b"ab~{\x79\x79\x41\x44~}cd", "replace", "ab\ufffd\ufffd\u804acd"),
+        # issue24117
+        ('hi~', 'strict',  b'hi~~'), # escape ~
+        (b'~{Dc~~:C~}', 'strict', None), # ~~ only in ASCII mode
+        (b'~{Dc~\n:C~}', 'strict', None), # ~\n only in ASCII mode
     )
 
 def test_main():
diff -r c79fd57f86b6 Modules/cjkcodecs/_codecs_cn.c
--- a/Modules/cjkcodecs/_codecs_cn.c
+++ b/Modules/cjkcodecs/_codecs_cn.c
@@ -279,7 +279,8 @@ DECODER(gb18030)
             REQUIRE_INBUF(4);
             c3 = INBYTE3;
             c4 = INBYTE4;
-            if (c < 0x81 || c3 < 0x81 || c4 < 0x30 || c4 > 0x39)
+            if (c < 0x81 || c > 0xFE || c3 < 0x81 || c3 > 0xFE ||
+                c4 < 0x30 || c4 > 0x39)
                 return 1;
             c -= 0x81;  c2 -= 0x30;
             c3 -= 0x81; c4 -= 0x30;
@@ -348,14 +349,27 @@ ENCODER(hz)
         DBCHAR code;
 
         if (c < 0x80) {
-            if (state->i == 0) {
-                WRITEBYTE1((unsigned char)c);
-                NEXT(1, 1);
+            if (c == '~') {
+                if (state->i == 0) {
+                    WRITEBYTE2('~', '~');
+                    NEXT(1, 2);
+                }
+                else {
+                    WRITEBYTE4('~', '}', '~', '~');
+                    NEXT(1, 4);
+                    state->i = 0;
+                }
             }
             else {
-                WRITEBYTE3('~', '}', (unsigned char)c);
-                NEXT(1, 3);
-                state->i = 0;
+                if (state->i == 0) {
+                    WRITEBYTE1((unsigned char)c);
+                    NEXT(1, 1);
+                }
+                else {
+                    WRITEBYTE3('~', '}', (unsigned char)c);
+                    NEXT(1, 3);
+                    state->i = 0;
+                }
             }
             continue;
         }
@@ -404,19 +418,18 @@ DECODER(hz)
         Py_UCS4 decoded;
 
         if (c == '~') {
-            unsigned char c2 = INBYTE2;
+            unsigned char c2;
 
             REQUIRE_INBUF(2);
-            if (c2 == '~') {
-                OUTCHAR('~');
-                NEXT_IN(2);
-                continue;
-            }
-            else if (c2 == '{' && state->i == 0)
+            c2 = INBYTE2;
+
+            if (c2 == '{' && state->i == 0)
                 state->i = 1; /* set GB */
             else if (c2 == '}' && state->i == 1)
                 state->i = 0; /* set ASCII */
-            else if (c2 == '\n')
+            else if (c2 == '~' && state->i == 0)
+                OUTCHAR('~');
+            else if (c2 == '\n' && state->i == 0)
                 ; /* line-continuation */
             else
                 return 1;
diff -r c79fd57f86b6 Modules/cjkcodecs/README
--- a/Modules/cjkcodecs/README
+++ b/Modules/cjkcodecs/README
@@ -77,3 +77,54 @@ Notes on implmentation characteristics of each cod
    - U+007E TILDE is mapped to SHIFT-JIS 0x7e.
    - U+FF3C FULL-WIDTH REVERSE SOLIDUS is mapped to SHIFT-JIS 815f.
 
+
+6) GB2312 codec
+
+  There exist two implementations of GB2312 differently in two code points.
+
+  bytes    Implementation A    Implementation B
+  A1A4     U+00B7 MIDDLE DOT   U+30FB KATAKANA MIDDLE DOT
+  A1AA     U+2014 EM DASH      U+2015 HORIZONTAL BAR
+
+  Implementation A is compatible with GBK and GB18030, while Implementation
+  B is not.
+
+  Python 2.x/3.x are using Implementation B.
+  
+  As of 2015, Microsoft .Net Framework is using Implementation A.
+  iconv-1.14, php-5.6, ActivePerl-5.20, Java-1.7 are using Implementation B.
+  Ruby-2.2 is compatible with both Implementation A and Implementation B, it
+  internally converts the conflictive characters to Implementation A.
+
+
+7) GBK codec
+
+  This implmentation can be seem as either "GBK without PUA code points",
+  or "CP936 v2.01 without euro sign (0x80 <-> U+20AC)".
+
+  GBK standard gave a total of 23940 two-byte sequences, 2149 of them
+  were mapped to PUA of BMP. In this implmentation, these 2149 sequences
+  were discarded, so this implmentation has 21791 (=23940-2149) two-byte
+  sequences.
+  
+  The 2149 (=2054+95) sequences are mapped to 0xE000-0xE864 in PUA.
+
+  The 2054 are empty positions, nothing was assigned to these positions.
+
+  The 95 were assigned with characters. When GBK standard was published
+  in 1995, these 95 characters were not included by Unicode, so mapped
+  them to PUA. They are included by later version of Unicode.
+
+
+8) GB18030 codec
+
+  This codec implemented full GB18030-2000 standard.
+  25 characters were mapped to PUA of BMP.
+
+
+  To implement full GB18030-2005 codec, just modify as below:
+
+  bytes        GB18030-2000   GB18030-2005
+  A8BC         U+E7C7         U+1E3F
+  8135F437     U+1E3F         U+E7C7
+  * U+1E3F is "LATIN SMALL LETTER M WITH ACUTE".