Add encrypted .bgm [Nanami to Konomi no Oshiete ABC (PC)]

src/libvgmstream.vcproj

@@ -292,6 +292,10 @@
                     RelativePath=".\meta\ea_schl_streamfile.h"
                     >
                 </File>
+                <File
+                    RelativePath=".\meta\encrypted_bgm_streamfile.h"
+                    >
+                </File>
                 <File
                     RelativePath=".\meta\fsb_encrypted_streamfile.h"
                     >
@@ -1271,7 +1275,7 @@
 					>
 				</File>
 				<File
-					RelativePath=".\meta\ps2_exst.c"
+					RelativePath=".\meta\exst.c"
 					>
 				</File>
 				<File

src/libvgmstream.vcxproj

@@ -115,6 +115,7 @@
     <ClInclude Include="meta\ea_eaac_streamfile.h" />
     <ClInclude Include="meta\ea_eaac_opus_streamfile.h" />
     <ClInclude Include="meta\ea_schl_streamfile.h" />
+    <ClInclude Include="meta\encrypted_bgm_streamfile.h" />
     <ClInclude Include="meta\fsb_encrypted_streamfile.h" />
     <ClInclude Include="meta\fsb_interleave_streamfile.h" />
     <ClInclude Include="meta\fsb5_streamfile.h" />
@@ -445,7 +446,7 @@
     <ClCompile Include="meta\ps2_ccc.c" />
     <ClCompile Include="meta\ps2_dxh.c" />
     <ClCompile Include="meta\ps2_enth.c" />
-    <ClCompile Include="meta\ps2_exst.c" />
+    <ClCompile Include="meta\exst.c" />
     <ClCompile Include="meta\ps2_filp.c" />
     <ClCompile Include="meta\ps2_gbts.c" />
     <ClCompile Include="meta\ps2_gcm.c" />

src/libvgmstream.vcxproj.filters

@@ -110,6 +110,9 @@
     <ClInclude Include="meta\ea_schl_streamfile.h">
       <Filter>meta\Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="meta\encrypted_bgm_streamfile">
+      <Filter>meta\Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="meta\fsb_encrypted_streamfile.h">
       <Filter>meta\Header Files</Filter>
     </ClInclude>
@@ -832,7 +835,7 @@
     <ClCompile Include="meta\ps2_enth.c">
       <Filter>meta\Source Files</Filter>
     </ClCompile>
-    <ClCompile Include="meta\ps2_exst.c">
+    <ClCompile Include="meta\exst.c">
       <Filter>meta\Source Files</Filter>
     </ClCompile>
     <ClCompile Include="meta\ps2_filp.c">

src/meta/encrypted.c

@@ -1,6 +1,7 @@
 #include "meta.h"
 #include "../coding/coding.h"
 #include "ogg_vorbis_streamfile.h"
+#include "encrypted_bgm_streamfile.h"
 
 //todo fuse ogg encryptions and use generic names
 
@@ -80,6 +81,32 @@ VGMSTREAM* init_vgmstream_encrypted(STREAMFILE* sf) {
         return vgmstream;
     }
 
+    if (check_extensions(sf,"bgm")) {
+        uint8_t keybuf[0x100];
+        size_t key_size;
+        off_t start;
+
+        /* Studio Ring games [Nanami to Konomi no Oshiete ABC (PC), Oyatsu no Jikan (PC)] */
+        if (id != get_id32be("RIFF"))
+            goto fail;
+
+        /* Standard RIFF xor'd past "data", sometimes including extra chunks like JUNK or smpl.
+         * If .bgm is added to riff.c this needs to be reworked so detection goes first, or bgm+bgmkey is
+         * rejected in riff.c (most files are rejected due to the xor'd extra chunks though). */
+        key_size = read_key_file(keybuf, sizeof(keybuf), sf);
+        if (key_size <= 0) goto fail;
+
+        if (!find_chunk_le(sf, get_id32be("data"), 0x0c, 0, &start, NULL))
+            goto fail;
+
+        temp_sf = setup_bgm_streamfile(sf, start, keybuf, key_size);
+        if (!temp_sf) goto fail;
+
+        vgmstream = init_vgmstream_riff(temp_sf);
+        close_streamfile(temp_sf);
+        return vgmstream;
+    }
+
 
 fail:
     return NULL;

src/meta/encrypted_bgm_streamfile.h

@@ -0,0 +1,52 @@
+#ifndef _BGM_STREAMFILE_H_
+#define _BGM_STREAMFILE_H_
+#include "../streamfile.h"
+
+
+typedef struct {
+    uint8_t key[0x100];
+    size_t key_len;
+    off_t start;
+} bgm_io_data;
+
+static size_t bgm_io_read(STREAMFILE *sf, uint8_t *dest, off_t offset, size_t length, bgm_io_data* data) {
+    int i, begin, pos;
+    size_t bytes = read_streamfile(dest, offset, length, sf);
+
+    /* decrypt data (xor) */
+    if (offset + length > data->start) {
+        if (offset < data->start) {
+            begin = data->start - offset;
+            pos = 0;
+        }
+        else {
+            begin = 0;
+            pos = offset - data->start;
+        }
+
+        for (i = begin; i < bytes; i++) {
+            dest[i] ^= data->key[(pos++) % data->key_len];
+        }
+    }
+
+    return bytes;
+}
+
+/* decrypts BGM stream */
+static STREAMFILE* setup_bgm_streamfile(STREAMFILE *sf, off_t start, uint8_t* key, int key_len) {
+    STREAMFILE *new_sf = NULL;
+    bgm_io_data io_data = {0};
+
+    io_data.start = start;
+    io_data.key_len = key_len;
+    if (key_len > sizeof(io_data.key))
+        return NULL;
+    memcpy(io_data.key, key, key_len);
+
+    new_sf = open_wrap_streamfile(sf);
+    new_sf = open_io_streamfile_f(new_sf, &io_data, sizeof(bgm_io_data), bgm_io_read, NULL);
+    new_sf = open_fakename_streamfile_f(new_sf, NULL, "wav");
+    return new_sf;
+}
+
+#endif /* _BGM_STREAMFILE_H_ */