(Lianja) Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats.

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// Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

// Private-Key: (256 bit)
// priv:
//     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
//     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
//     87:2d
// pub:
//     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
//     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
//     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
//     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
//     12:b7:b8:6a:43
// ASN1 OID: prime256v1
// NIST CURVE: P-256
// writing EC key
// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----

// The public key is shown in two different formats.
// The first is this:

// pub:
//     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
//     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
//     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
//     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
//     12:b7:b8:6a:43

// It is the ANSI X9.63 format.
// 65-bytes are the uncompressed public key (04 || X || Y) 

// This is the same public key, but in PEM format

// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----

// It contains ASN.1 that more explicitly identifies the key type.
// 
// SEQUENCE (2 elem)
//   SEQUENCE (2 elem)
//     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
//     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
//   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

// PEM format can be loaded into a Chilkat public key object like this:

loSbPem = createobject("CkStringBuilder")
loSbPem.Append("-----BEGIN PUBLIC KEY-----" + Chr(13) + Chr(10))
loSbPem.Append("MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET" + Chr(13) + Chr(10))
loSbPem.Append("Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==" + Chr(13) + Chr(10))
loSbPem.Append("-----END PUBLIC KEY-----" + Chr(13) + Chr(10))

loPubKey1 = createobject("CkPublicKey")
llSuccess = loPubKey1.LoadFromString(loSbPem.GetAsString())
if (llSuccess = .F.) then
    ? loPubKey1.LastErrorText
    release loSbPem
    release loPubKey1
    return
endif

// The X9.63 format can be loaded like this:
loSbHex = createobject("CkStringBuilder")
loSbHex.Append("04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:")
loSbHex.Append("b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:")
loSbHex.Append("39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:")
loSbHex.Append("2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:")
loSbHex.Append("12:b7:b8:6a:43")

// Get rid of the ":" chars.
lnNumReplaced = loSbHex.Replace(":","")

// We'll need to convert hex to base64..
loBdKey = createobject("CkBinData")
loBdKey.AppendEncoded(loSbHex.GetAsString(),"hex")

loPubKey2 = createobject("CkPublicKey")
llSuccess = loPubKey2.LoadFromString(loBdKey.GetEncoded("base64"))
if (llSuccess = .F.) then
    ? loPubKey2.LastErrorText
    release loSbPem
    release loPubKey1
    release loSbHex
    release loBdKey
    release loPubKey2
    return
endif

// Let's get the key in pubKey2 as PEM.
// It should be idential to the PEM above.
? loPubKey2.GetPem(.T.)

// Here's the output.  You can see it's the same as the PEM above..

// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----


release loSbPem
release loPubKey1
release loSbHex
release loBdKey
release loPubKey2