Signing and Signature Verification Overview and Algorithm Specifications

The digital signature can be used to verify whether the data came from the stated sender and has been changed.

This topic describes the supported algorithms and specifications for signing and signature verification.

RSA

The Crypto framework supports the following padding modes for RSA signing and signature verification:

• PKCS1: RSAES-PKCS1-V1_5 mode in RFC3447, corresponding to RSA_PKCS1_PADDING in OpenSSL.

  When this padding mode is used, the message digest (md) must be set, and the length of the MD must be less than that of the RSA modulus n, in bytes.

• PSS: RSASSA-PSS mode in RFC 3447, corresponding to RSA_PKCS1_PSS_PADDING in OpenSSL.

  If this padding mode is used, two message digests (md and mgf1_md) must be set, and the total length of md and mgf1_md must be less than the length of the RSA key modulus.

  You can also set the salt length saltLen to obtain PSS-related parameters.

PKCS1

When creating an RSA asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter. The string parameter consists of the asymmetric key type, padding mode PKCS1, and MD algorithm with a vertical bar (|) in between.

In the following table, the options included in the square brackets ([]) are mutually exclusive. You can use only one of them in a string parameter. For example, if the asymmetric key type is RSA512, the padding mode is PKCS1, and the MD algorithm is MD5, the string parameter is RSA512|PKCS1|MD5.

NOTE In RSA signing and signature verification, the MD length must be less than the length of the RSA modulus (n). For example, if the RSA key is 512 bits, SHA512 cannot be used.

As indicated by the last row in the preceding table, you can specify the RSA key type without the key length to ensure compatibility with the key generated based on the key parameter. In this case, the signing or signature verification operation varies depending on the actual key length.

PSS

When creating an RSA asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter. The string parameter consists of the asymmetric key type, padding mode PSS, MD, and mask digest with a vertical bar (|) in between.

In the following table, the options included in the square brackets ([]) are mutually exclusive. You can use only one of them in a string parameter. For example, if the asymmetric key type is RSA2048, the padding mode is PSS, the MD algorithm is SHA256, and the mask digest is MGF1_SHA256, the string parameter is RSA2048|PSS|SHA256|MGF1_SHA256.

NOTE If PSS padding mode is used in RSA signing or signature verification, the total length of md and mgf1_md must be less than the length of the RSA modulus. For example, if the RSA key is 512 bits, md and mgf1_md cannot be SHA256 at the same time.

As indicated by the last row in the preceding table, you can specify the RSA key type without the key length to ensure compatibility with the key generated based on the key parameter. In this case, the signing or signature verification operation varies depending on the actual key length.

Getting and Setting of PSS Parameters

The following table lists the parameters that can be set or obtained when the PSS mode is used. The symbol "√" indicates that the parameter can be obtained or set.

ECDSA

Elliptic Curve Digital Signature Algorithm (ECDSA) is a digital signature algorithm (DSA) based on Elliptic Curve Cryptography (ECC). Compared with the ordinary Discrete Logarithm Problem (DLP) and Integer Factorization Problem (IFP), the ECC provides a higher unit bit strength than other public-key cryptographic systems.

The Crypto Framework provides ECDSA signing and signature verification capabilities that combine a variety of elliptic curves and digest algorithms.

When creating an ECDSA asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter. The string parameter consists of the asymmetric key type and MD with a vertical bar (|) in between.

In the following table, the options included in the square brackets ([]) are mutually exclusive. You can use only one of them in a string parameter. For example, if the asymmetric key type is ECC224 and the MD algorithm is SHA256, the string parameter is ECC224|SHA256.

As indicated by the last row in the preceding table, you can specify the key type without the key length and curve name to ensure compatibility with the key generated based on the key parameter. In this case, the signing or signature verification operation varies depending on the actual key length.

DSA

The Digital Signature Algorithm (DSA) stands out with great compatibility and applicability.

When creating a DSA asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter. The string parameter consists of the asymmetric key type and MD with a vertical bar (|) in between.

In the following table, the options included in the square brackets ([]) are mutually exclusive. You can use only one of them in a string parameter. For example, if the asymmetric key type is DSA1024 and the MD algorithm is SHA256, the string parameter is DSA1024|SHA256.

As indicated by the last row in the preceding table, you can specify the DSA key type without the key length to ensure compatibility with the key generated based on the key parameter. In this case, the signing or signature verification operation varies depending on the actual key length.

SM2

SM2 is a digital signature algorithm based on ECC.

When creating an SM2 asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter. The string parameter consists of the asymmetric key type and MD with a vertical bar (|) in between.

Currently, SM2 signing support only SM3.

As indicated by the last row in the preceding table, you can specify the SM2 key type without the key length to ensure compatibility with the key generated based on the key parameter. In this case, the signing or signature verification operation varies depending on the actual key length.

Ed25519

Ed25519 is a signing and signature verification algorithm based on the ECC.

When creating an Ed25519 asymmetric signing (Sign) or signature verification (Verify) instance, you need to specify the algorithm specifications in a string parameter.