What is SHA-256 (Secure Hash Algorithm 2 - 256 bits) Certificate?

SHASHA-256 (Secure Hash Algorithm 2 - 256 bits) Certificate is a X.509 certificate that uses SHA-1 hash function to generate the hash of the public key provided by the certificate subject.

Here is an example of a SHA-1 certificate:

fyicenter$ openssl x509 -in GlobalSign.pem -text -noout

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            04:00:00:00:00:01:0f:86:26:e6:0d
        Signature Algorithm: sha1WithRSAEncryption
        Issuer: OU = GlobalSign Root CA - R2, O = GlobalSign, CN = GlobalSign
        Validity
            Not Before: Dec 15 08:00:00 2006 GMT
            Not After : Dec 15 08:00:00 2021 GMT
        Subject: OU = GlobalSign Root CA - R2, O = GlobalSign, CN = GlobalSign
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:a6:cf:24:0e:be:2e:6f:28:99:45:42:c4:ab:3e:
                    21:54:9b:0b:d3:7f:84:70:fa:12:b3:cb:bf:87:5f:
                    c6:7f:86:d3:b2:30:5c:d6:fd:ad:f1:7b:dc:e5:f8:
                    60:96:09:92:10:f5:d0:53:de:fb:7b:7e:73:88:ac:
                    52:88:7b:4a:a6:ca:49:a6:5e:a8:a7:8c:5a:11:bc:
                    7a:82:eb:be:8c:e9:b3:ac:96:25:07:97:4a:99:2a:
                    07:2f:b4:1e:77:bf:8a:0f:b5:02:7c:1b:96:b8:c5:
                    b9:3a:2c:bc:d6:12:b9:eb:59:7d:e2:d0:06:86:5f:
                    5e:49:6a:b5:39:5e:88:34:ec:bc:78:0c:08:98:84:
                    6c:a8:cd:4b:b4:a0:7d:0c:79:4d:f0:b8:2d:cb:21:
                    ca:d5:6c:5b:7d:e1:a0:29:84:a1:f9:d3:94:49:cb:
                    24:62:91:20:bc:dd:0b:d5:d9:cc:f9:ea:27:0a:2b:
                    73:91:c6:9d:1b:ac:c8:cb:e8:e0:a0:f4:2f:90:8b:
                    4d:fb:b0:36:1b:f6:19:7a:85:e0:6d:f2:61:13:88:
                    5c:9f:e0:93:0a:51:97:8a:5a:ce:af:ab:d5:f7:aa:
                    09:aa:60:bd:dc:d9:5f:df:72:a9:60:13:5e:00:01:
                    c9:4a:fa:3f:a4:ea:07:03:21:02:8e:82:ca:03:c2:
                    9b:8f
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage: critical
                Certificate Sign, CRL Sign
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Subject Key Identifier: 
                9B:E2:07:57:67:1C:1E:C0:6A:06:DE:59:B4:9A:2D:DF:DC:19:86:2E
            X509v3 CRL Distribution Points: 

                Full Name:
                  URI:http://crl.globalsign.net/root-r2.crl

            X509v3 Authority Key Identifier: 
                keyid:9B:E2:07:57:67:1C:1E:C0:6A:06:DE:59:B4:9A:2D:DF:DC:19:86:2E

    Signature Algorithm: sha1WithRSAEncryption
         99:81:53:87:1c:68:97:86:91:ec:e0:4a:b8:44:0b:ab:81:ac:
         27:4f:d6:c1:b8:1c:43:78:b3:0c:9a:fc:ea:2c:3c:6e:61:1b:
         4d:4b:29:f5:9f:05:1d:26:c1:b8:e9:83:00:62:45:b6:a9:08:
         93:b9:a9:33:4b:18:9a:c2:f8:87:88:4e:db:dd:71:34:1a:c1:
         54:da:46:3f:e0:d3:2a:ab:6d:54:22:f5:3a:62:cd:20:6f:ba:
         29:89:d7:dd:91:ee:d3:5c:a2:3e:a1:5b:41:f5:df:e5:64:43:
         2d:e9:d5:39:ab:d2:a2:df:b7:8b:d0:c0:80:19:1c:45:c0:2d:
         8c:e8:f8:2d:a4:74:56:49:c5:05:b5:4f:15:de:6e:44:78:39:
         87:a8:7e:bb:f3:79:18:91:bb:f4:6f:9d:c1:f0:8c:35:8c:5d:
         01:fb:c3:6d:b9:ef:44:6d:79:46:31:7e:0a:fe:a9:82:c1:ff:
         ef:ab:6e:20:c4:50:c9:5f:9d:4d:9b:17:8c:0c:e5:01:c9:a0:
         41:6a:73:53:fa:a5:50:b4:6e:25:0f:fb:4c:18:f4:fd:52:d9:
         8e:69:b1:e8:11:0f:de:88:d8:fb:1d:49:f7:aa:de:95:cf:20:
         78:c2:60:12:db:25:40:8c:6a:fc:7e:42:38:40:64:12:f7:9e:
         81:e1:93:2e

As you can see, the "Signature Algorithm: sha1WithRSAEncryption" field tells us that this "GlobalSign Root CA - R2" root CA certificate is a SHA-1 certificate. It is considered as not secure.

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