std.crypto: add constant-time codecs (#23420)

std.crypto: add constant-time codecs

Add constant-time hex/base64 codecs designed to process cryptographic
secrets, adapted from libsodium's implementations.

Introduce a `crypto.codecs` namespace for crypto-related encoders and
decoders. Move ASN.1 codecs to this namespace.

This will also naturally accommodate the proposed PEM codecs.

Author: jedisct1

.gitattributes

@@ -5,6 +5,7 @@ langref.html.in text eol=lf
 lib/std/compress/testdata/** binary
 lib/std/compress/deflate/testdata/** binary
 lib/std/compress/flate/testdata/** binary
+lib/std/crypto/codecs/asn1/der/testdata/** binary
 
 lib/include/** linguist-vendored
 lib/libc/** linguist-vendored

lib/std/crypto.zig

@@ -214,13 +214,15 @@ pub const ff = @import("crypto/ff.zig");
 /// This is a thread-local, cryptographically secure pseudo random number generator.
 pub const random = @import("crypto/tlcsprng.zig").interface;
 
+/// Encoding and decoding
+pub const codecs = @import("crypto/codecs.zig");
+
 const std = @import("std.zig");
 
 pub const errors = @import("crypto/errors.zig");
 
 pub const tls = @import("crypto/tls.zig");
 pub const Certificate = @import("crypto/Certificate.zig");
-pub const asn1 = @import("crypto/asn1.zig");
 
 /// Side-channels mitigations.
 pub const SideChannelsMitigations = enum {
@@ -335,7 +337,7 @@ test {
     _ = errors;
     _ = tls;
     _ = Certificate;
-    _ = asn1;
+    _ = codecs;
 }
 
 test "CSPRNG" {

lib/std/crypto/codecs.zig

@@ -0,0 +1,3 @@
+pub const asn1 = @import("codecs/asn1.zig");
+pub const Base64 = @import("codecs/base64_hex_ct.zig").Base64;
+pub const Hex = @import("codecs/base64_hex_ct.zig").Hex;