From: lei he <[email protected]>
The signature of ECDSA is consists of two big integers up to the
size of keylen, and is DER encoded into one SEQUENCE.
Calculate max_size of ECDSA signature more accurately according to
the DER encoding rules.
Signed-off-by: lei he <[email protected]>
---
crypto/Kconfig | 1 +
crypto/Makefile | 2 ++
crypto/ecdsa.c | 3 ++-
crypto/ecdsa_helper.c | 45 +++++++++++++++++++++++++++++++++
include/crypto/internal/ecdsa.h | 15 +++++++++++
include/linux/asn1_encoder.h | 2 ++
lib/asn1_encoder.c | 3 ++-
7 files changed, 69 insertions(+), 2 deletions(-)
create mode 100644 crypto/ecdsa_helper.c
create mode 100644 include/crypto/internal/ecdsa.h
diff --git a/crypto/Kconfig b/crypto/Kconfig
index 19197469cfab..3e82c7bc8424 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -254,6 +254,7 @@ config CRYPTO_ECDSA
select CRYPTO_ECC
select CRYPTO_AKCIPHER
select ASN1
+ select ASN1_ENCODER
help
Elliptic Curve Digital Signature Algorithm (NIST P192, P256 etc.)
is A NIST cryptographic standard algorithm. Only signature verification
diff --git a/crypto/Makefile b/crypto/Makefile
index 43bc33e247d1..226bc2cfb9b7 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -52,8 +52,10 @@ obj-$(CONFIG_CRYPTO_SM2) += sm2_generic.o
$(obj)/ecdsasignature.asn1.o: $(obj)/ecdsasignature.asn1.c $(obj)/ecdsasignature.asn1.h
$(obj)/ecdsa.o: $(obj)/ecdsasignature.asn1.h
+
ecdsa_generic-y += ecdsa.o
ecdsa_generic-y += ecdsasignature.asn1.o
+ecdsa_generic-y += ecdsa_helper.o
obj-$(CONFIG_CRYPTO_ECDSA) += ecdsa_generic.o
crypto_acompress-y := acompress.o
diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
index b3a8a6b572ba..2ba44c92d271 100644
--- a/crypto/ecdsa.c
+++ b/crypto/ecdsa.c
@@ -6,6 +6,7 @@
#include <linux/module.h>
#include <crypto/internal/akcipher.h>
#include <crypto/internal/ecc.h>
+#include <crypto/internal/ecdsa.h>
#include <crypto/akcipher.h>
#include <crypto/ecdh.h>
#include <linux/asn1_decoder.h>
@@ -262,7 +263,7 @@ static unsigned int ecdsa_max_size(struct crypto_akcipher *tfm)
{
struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
- return ctx->pub_key.ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+ return ecdsa_max_signature_size(ctx->curve);
}
static int ecdsa_nist_p384_init_tfm(struct crypto_akcipher *tfm)
diff --git a/crypto/ecdsa_helper.c b/crypto/ecdsa_helper.c
new file mode 100644
index 000000000000..487c4e9c0f67
--- /dev/null
+++ b/crypto/ecdsa_helper.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RSA key extract helper
+ *
+ * Copyright 2022 Bytedance CO., LTD.
+ *
+ * Authors: lei he <[email protected]>
+ */
+#include <crypto/internal/ecdsa.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/oid_registry.h>
+#include <linux/asn1_encoder.h>
+#include <crypto/ecdh.h>
+
+unsigned int ecdsa_max_signature_size(const struct ecc_curve *curve)
+{
+ unsigned int keylen = curve->g.ndigits * sizeof(u64);
+ /* Up to one extra byte to indicate the format */
+ unsigned char buffer[sizeof(size_t) + 1], *data = buffer;
+ int buffer_len = sizeof(buffer);
+ unsigned int coordinate_length, sequence_length;
+
+ asn1_encode_length(&data, &buffer_len, keylen);
+ /**
+ * The extra cost for encoding keylen bytes as INTEGER in ASN.1:
+ * 1. one byte for tag
+ * 2. sizeof(buffer) - buffer_len bytes for length
+ * 3. one leading zero byte for integers whose leftmost bit is 1
+ */
+ coordinate_length = 1 + sizeof(buffer) - buffer_len + 1 + keylen;
+
+ /**
+ * The extra cost for encoding coordinate_length * 2 bytes as SEQUENCE in ASN.1:
+ * 1. one byte for tag
+ * 2. sizeof(buffer) - buffer_len bytes for length
+ */
+ buffer_len = sizeof(buffer);
+ data = buffer;
+ asn1_encode_length(&data, &buffer_len, coordinate_length * 2);
+ sequence_length = 1 + sizeof(buffer) - buffer_len + coordinate_length * 2;
+
+ return sequence_length;
+}
+EXPORT_SYMBOL_GPL(ecdsa_max_signature_size);
diff --git a/include/crypto/internal/ecdsa.h b/include/crypto/internal/ecdsa.h
new file mode 100644
index 000000000000..e35638a35dc2
--- /dev/null
+++ b/include/crypto/internal/ecdsa.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * ECDSA internal helpers
+ *
+ * Copyright (c) 2022 lei he <[email protected]>
+ */
+
+ #ifndef _CRYPTO_ECDSA_H
+ #define _CRYPTO_ECDSA_H
+
+#include <crypto/ecc_curve.h>
+
+unsigned int ecdsa_max_signature_size(const struct ecc_curve *curve);
+
+#endif
diff --git a/include/linux/asn1_encoder.h b/include/linux/asn1_encoder.h
index 08cd0c2ad34f..fe439c9a73e3 100644
--- a/include/linux/asn1_encoder.h
+++ b/include/linux/asn1_encoder.h
@@ -29,4 +29,6 @@ unsigned char *
asn1_encode_boolean(unsigned char *data, const unsigned char *end_data,
bool val);
+int asn1_encode_length(unsigned char **data, int *data_len, int len);
+
#endif
diff --git a/lib/asn1_encoder.c b/lib/asn1_encoder.c
index 0fd3c454a468..644af3055ebb 100644
--- a/lib/asn1_encoder.c
+++ b/lib/asn1_encoder.c
@@ -188,7 +188,7 @@ EXPORT_SYMBOL_GPL(asn1_encode_oid);
* encoder primitives to accept negative lengths as singalling the
* sequence will be re-encoded when the length is known.
*/
-static int asn1_encode_length(unsigned char **data, int *data_len, int len)
+int asn1_encode_length(unsigned char **data, int *data_len, int len)
{
if (*data_len < 1)
return -EINVAL;
@@ -239,6 +239,7 @@ static int asn1_encode_length(unsigned char **data, int *data_len, int len)
return 0;
}
+EXPORT_SYMBOL_GPL(asn1_encode_length);
/**
* asn1_encode_tag() - add a tag for optional or explicit value
--
2.20.1