diff --git a/lib/std/crypto/codecs.zig b/lib/std/crypto/codecs.zig
index 7cf92b1117ff..21be2dda186e 100644
--- a/lib/std/crypto/codecs.zig
+++ b/lib/std/crypto/codecs.zig
@@ -1,3 +1,8 @@
 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;
+
+test {
+    _ = @import("codecs/asn1.zig");
+    _ = @import("codecs/base64_hex_ct.zig");
+}
diff --git a/lib/std/crypto/codecs/asn1.zig b/lib/std/crypto/codecs/asn1.zig
index 968ef1161a18..0b4c50644c30 100644
--- a/lib/std/crypto/codecs/asn1.zig
+++ b/lib/std/crypto/codecs/asn1.zig
@@ -90,7 +90,7 @@ pub const Tag = struct {
         };
     }
 
-    pub fn encode(self: Tag, writer: *std.Io.Writer) @TypeOf(writer).Error!void {
+    pub fn encode(self: Tag, writer: *std.Io.Writer) std.Io.Writer.Error!void {
         var tag1 = FirstTag{
             .number = undefined,
             .constructed = self.constructed,
@@ -98,7 +98,7 @@ pub const Tag = struct {
         };
 
         var buffer: [3]u8 = undefined;
-        var writer2: std.Io.Writer = .init(&buffer);
+        var writer2: std.Io.Writer = .fixed(&buffer);
 
         switch (@intFromEnum(self.number)) {
             0...std.math.maxInt(u5) => |n| {
@@ -183,7 +183,7 @@ pub const Element = struct {
         }
     };
 
-    pub const DecodeError = error{ InvalidLength, EndOfStream };
+    pub const DecodeError = error{ InvalidLength, EndOfStream, ReadFailed };
 
     /// Safely decode a DER/BER/CER element at `index`:
     /// - Ensures length uses shortest form
diff --git a/lib/std/crypto/codecs/asn1/Oid.zig b/lib/std/crypto/codecs/asn1/Oid.zig
index be5bc7e7ff8b..4f3f36236290 100644
--- a/lib/std/crypto/codecs/asn1/Oid.zig
+++ b/lib/std/crypto/codecs/asn1/Oid.zig
@@ -47,7 +47,7 @@ test fromDot {
     }
 }
 
-pub fn toDot(self: Oid, writer: anytype) @TypeOf(writer).Error!void {
+pub fn toDot(self: Oid, writer: anytype) std.Io.Writer.Error!void {
     const encoded = self.encoded;
     const first = @divTrunc(encoded[0], 40);
     const second = encoded[0] - first * 40;
@@ -81,7 +81,7 @@ test toDot {
     for (test_cases) |t| {
         var stream: std.Io.Writer = .fixed(&buf);
         try toDot(Oid{ .encoded = t.encoded }, &stream);
-        try std.testing.expectEqualStrings(t.dot_notation, stream.written());
+        try std.testing.expectEqualStrings(t.dot_notation, stream.buffered());
     }
 }
 
diff --git a/lib/std/crypto/codecs/asn1/der/ArrayListReverse.zig b/lib/std/crypto/codecs/asn1/der/ArrayListReverse.zig
index b761a93345d0..c61b108d095c 100644
--- a/lib/std/crypto/codecs/asn1/der/ArrayListReverse.zig
+++ b/lib/std/crypto/codecs/asn1/der/ArrayListReverse.zig
@@ -7,18 +7,28 @@
 
 const std = @import("std");
 const Allocator = std.mem.Allocator;
+const Io = std.Io;
 const assert = std.debug.assert;
 const testing = std.testing;
 
 data: []u8,
 capacity: usize,
 allocator: Allocator,
+writer: Io.Writer,
 
 const ArrayListReverse = @This();
 const Error = Allocator.Error;
 
 pub fn init(allocator: Allocator) ArrayListReverse {
-    return .{ .data = &.{}, .capacity = 0, .allocator = allocator };
+    return .{
+        .data = &.{},
+        .capacity = 0,
+        .allocator = allocator,
+        .writer = .{
+            .buffer = &.{},
+            .vtable = &vtable,
+        },
+    };
 }
 
 pub fn deinit(self: *ArrayListReverse) void {
@@ -67,6 +77,67 @@ pub fn clearAndFree(self: *ArrayListReverse) void {
     self.capacity = 0;
 }
 
+const vtable: Io.Writer.VTable = .{
+    .drain = &drain,
+};
+
+fn drain(w: *Io.Writer, data: []const []const u8, splat: usize) Io.Writer.Error!usize {
+    const self: *ArrayListReverse = @fieldParentPtr("writer", w);
+
+    assert(w.buffered().len == 0);
+
+    if (data.len == 1 and splat == 1) {
+        @branchHint(.likely);
+        self.prependSlice(data[0]) catch return error.WriteFailed;
+        return data[0].len;
+    }
+
+    const count = Io.Writer.countSplat(data, splat);
+    self.ensureCapacity(self.data.len + count) catch return error.WriteFailed;
+    const end = self.data.ptr;
+    const begin = end - count;
+    var slice = begin[0..count];
+
+    for (data[0 .. data.len - 1]) |bytes| {
+        @memcpy(slice[0..bytes.len], bytes);
+        slice = slice[bytes.len..];
+    }
+    for (0..splat) |_| {
+        const bytes = data[data.len - 1];
+        @memcpy(slice[0..bytes.len], bytes);
+        slice = slice[bytes.len..];
+    }
+
+    self.data.ptr = begin;
+    self.data.len += count;
+    return count;
+}
+
+test drain {
+    var b: ArrayListReverse = .init(std.testing.allocator);
+    defer b.deinit();
+
+    var n = try b.writer.write(&.{ 1, 2, 3 });
+    try std.testing.expectEqual(3, n);
+    try std.testing.expectEqualSlices(u8, &.{ 1, 2, 3 }, b.data);
+
+    n = try b.writer.writeSplat(&.{
+        &.{ 4, 5, 6 },
+        &.{ 7, 8, 9 },
+    }, 2);
+    try std.testing.expectEqual(9, n);
+    try std.testing.expectEqualSlices(
+        u8,
+        &.{
+            4, 5, 6,
+            7, 8, 9,
+            7, 8, 9,
+            1, 2, 3,
+        },
+        b.data,
+    );
+}
+
 /// The caller owns the returned memory.
 /// Capacity is cleared, making deinit() safe but unnecessary to call.
 pub fn toOwnedSlice(self: *ArrayListReverse) Error![]u8 {
diff --git a/lib/std/crypto/codecs/asn1/der/Encoder.zig b/lib/std/crypto/codecs/asn1/der/Encoder.zig
index 82b7e62910ab..3151cac3ad19 100644
--- a/lib/std/crypto/codecs/asn1/der/Encoder.zig
+++ b/lib/std/crypto/codecs/asn1/der/Encoder.zig
@@ -117,8 +117,8 @@ pub fn tagBytes(self: *Encoder, tag_: Tag, bytes: []const u8) !void {
 }
 
 /// Warning: This writer writes backwards. `fn print` will NOT work as expected.
-pub fn writer(self: *Encoder) ArrayListReverse.Writer {
-    return self.buffer.writer();
+pub fn writer(self: *Encoder) *std.Io.Writer {
+    return &self.buffer.writer;
 }
 
 fn int(self: *Encoder, comptime T: type, value: T) !void {