2 files changed, 110 insertions, 0 deletions
diff --git a/pyecsca/codegen/asn1/asn1.c b/pyecsca/codegen/asn1/asn1.c
new file mode 100644
index 0000000..3fd1f5f
--- /dev/null
+++ b/pyecsca/codegen/asn1/asn1.c
@@ -0,0 +1,97 @@
+#include "asn1.h"
+
+#include <stdlib.h>
+
+uint8_t *asn1_der_encode(const bn_t *r, const bn_t *s, size_t *result_len) {
+    uint8_t r_len = (uint8_t) bn_to_bin_size(r);
+    uint8_t s_len = (uint8_t) bn_to_bin_size(s);
+
+	// Pad with one zero byte in case most-significant bit of top byte is one.
+    uint8_t r_length = r_len + (bn_get_bit(r, r_len * 8) ? 1 : 0);
+    uint8_t s_length = s_len + (bn_get_bit(s, s_len * 8) ? 1 : 0);
+
+    // R and S are < 128 bytes, so 1 byte tag + 1 byte len + len bytes value
+    size_t seq_value_len = 2 + r_length + 2 + s_length;
+    size_t whole_len = seq_value_len;
+
+    // The SEQUENCE length might be >= 128, so more bytes of length
+    size_t seq_len_len = 0;
+    if (seq_value_len >= 128) {
+        size_t s = seq_value_len;
+        do {
+            seq_len_len++;
+        } while ((s = s >> 8));
+    }
+    // seq_len_len bytes for length and one for length of length
+    whole_len += seq_len_len + 1;
+
+    // 1 byte tag for SEQUENCE
+    whole_len += 1;
+
+    uint8_t *data = malloc(whole_len);
+    size_t i = 0;
+    data[i++] = 0x30; // SEQUENCE
+    if (seq_value_len < 128) {
+        data[i++] = (uint8_t) seq_value_len;
+    } else {
+        data[i++] = (uint8_t) (seq_len_len | (1 << 7));
+        for (size_t j = 0; j < seq_len_len; ++j) {
+            data[i++] = (uint8_t) (seq_value_len & (0xff << (8 * (seq_len_len - j - 1))));
+        }
+    }
+    data[i++] = 0x02; //INTEGER
+    data[i++] = r_length;
+    if (bn_get_bit(r, r_len * 8)) {
+        data[i++] = 0;
+    }
+    bn_to_bin(r, data + i);
+    i += r_len;
+    data[i++] = 0x02; //INTEGER
+    data[i++] = s_length;
+    if (bn_get_bit(s, s_len * 8)) {
+        data[i++] = 0;
+    }
+    bn_to_bin(s, data + i);
+    i += s_len;
+
+    return data;
+}
+
+bool asn1_der_decode(const uint8_t *sig, size_t sig_len, bn_t *r, bn_t *s) {
+    size_t i = 0;
+    if (sig[i++] != 0x30) {//SEQUENCE
+        return false;
+    }
+    size_t seq_value_len = 0;
+    if (!(sig[i] & 0x80)) {
+        seq_value_len = sig[i++];
+    } else {
+        size_t seq_len_len = sig[i++] & 0x7f;
+        while (seq_len_len > 0) {
+            seq_value_len |= (sig[i++] << (seq_len_len - 1));
+            seq_len_len--;
+        }
+    }
+
+    if (sig[i++] != 0x02) {//INTEGER
+        return false;
+    }
+    size_t r_length = sig[i++];
+    size_t r_offset = i;
+    i += r_length;
+
+    if (sig[i++] != 0x02) {//INTEGER
+        return false;
+    }
+    size_t s_length = sig[i++];
+    size_t s_offset = i;
+    i += s_length;
+
+    if (i != sig_len) {
+        return false;
+    }
+
+    bn_from_bin(sig + r_offset, r_length, r);
+	bn_from_bin(sig + s_offset, s_length, s);
+    return true;
+}
+\ No newline at end of file
diff --git a/pyecsca/codegen/asn1/asn1.h b/pyecsca/codegen/asn1/asn1.h
new file mode 100644
index 0000000..691755c
--- /dev/null
+++ b/pyecsca/codegen/asn1/asn1.h
@@ -0,0 +1,13 @@
+#ifndef ASN1_H_
+#define ASN1_H_
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include "bn.h"
+
+uint8_t *asn1_der_encode(const bn_t *r, const bn_t *s, size_t *result_len);
+
+bool asn1_der_decode(const uint8_t *sig, size_t sig_len, bn_t *r, bn_t *s);
+
+#endif //ASN1_H_
+\ No newline at end of file